Short answer stay but work only within your role and look for a better new job.
Firstly you will have a load of transferrable skills and long term will be able to find a job which fits you needs. It may not be the same as your current neich role bit there are a number of jobs which your skillset will fit.
NB go to your GP and get help as no one should be so distressed over their job.
the atmosphere at work is dreadful.
This is totally normal when massive disruptive change of any kind happens. Add in people have been stressing over their jobs and are seeing others loose jobs then just going to work will be hard and stressful.
The mess will sort itself out and begin to settle into the new normal. Even after new process begin the changes will continue to throw up problems for a business cycle or two.
So you need to step back and pace yourself having a emotional connection to the company or the work is over investing yourself.
Senior managers have shown that they do not value the input of the people(you) involved in managing the change. You "owe" them nothing other than doing your role per your contract.
Sorry to be blunt but anyone on 45k is not "management" level in a big organisation.
You need to understand at the end of the day you work for Custardapples Ltd not Big Org Ltd.
You as CEO of Custardapples Ltd subcontract your time to BOL but have a responsibility to make sure that your business is a going concern.
To be a going concern you need to be healthy and have good mental health by NB understand your limitations. And understanding the contract terms you signed up to.
You are not a profit participant in BOL you are a cost element which is required to maximize their profits.
You are being contracted to do the same job as you were doing before the cost savings excercise that BOL decided was in their best interest.
The cost cutting exercise said that your role should stay the same and be paid out at the same 45k rate.
BOL will have paid the outside contractor multiples of your contract rate to create their plan. BOL had decided that the risks and the business failings which were highlighted were outweighed by the reward of profit.
On a positive note.
You were not paid to carry out the consultants work and you may not have had the same skill set yet in very crap working conditions you managed to produce a body of work which confirmed the consultant report.
Pat your self on the back for that body of work and revise your CV to reflect your skill and learning.
You’re already not sleeping and crying at the end of the day
Why are you doing this?
Your role is safe so its time to let go of the stress.
Are you the type who takes on ownership of problem situations or is the pressure coming from an external source?
You are not and were never a decision maker in the process. No matter how long or how hard you worked you were not going to be able to make any material change to the overall plan.
You got pulled into a process that you could not control or even infulance the outcome. Your senior managers did not even have the management skills to tell you that nothing was going to change the framework and that once started they were going to go through the motions to meet the legal requirements of a reorganisation.
You are Custardapples Ltd
If you pull out your job description and only do the tasks listed and nothing more will you still be paid?
If you double your workload and take on extra work will the company provide you with extra money?
If you solve the problems which will happen due to the change in the business do you get paid extra?
You need to step back into the role you are being paid for and mentally let go of the extras that you ended up taking on.
You need to work to get paid so that you can buy food and pay for your home. Keep in mind that your job is only a tool you use to do that.
Start each day by asking yourself is anything so important going to happen today that a year after you left that someone will be begging you to come back?
What is making you worry at night?
Why are you crying at the end of the day?
Is it the pressure from the lingering fear that you could have lost your job or is it something else?
Guilt that you still have a job when others lost theirs?
Or is the management expecting you to carry out a new role and work extra to solve the problems they created?
And on a general note do a money health check on where you are financially to see if you can reduce your worries on that front too.
I would suggest that you work on your CV and send it out.
You have "discovered" that a good work place is a key requirement to you enjoying your role so you need to think if you would change your role and job tasks to keep the good work culture.
Or would you move jobs and put up with a slightly less toxic workplace to keep your role?
You have a job which pays the bill so there is no race to get a new one. Take the time to find one which fits and be open to it being your current one if you can let go of the stress involved.
NB go to your GP asap.