In often make plans with my clients for exactly this kind of what if situation. We note them down on the records so people like your MIL are merely agreeing with your plan. The vast majority of the time we don't need to use the plan. Have a chat to your vet this really very common.
Well Sharm is too far to pop back if there is an issue and if you are not insured then you will lose the cost of the holiday. I think lonecat is right about speaking to your vet but personally I feel it's an awful burden for your MiL. You will also spend your holiday wondering and worrying. So sorry you have to make his decision
Oh Cervix love. I don't think he'll improve this time if you do it this way you will know you've been with him.
My mum left her dog with the usual sitters when she went away last year, but with strict instructions to contact me to go down and make any decisions. We also had a long on versatile as to whether she wanted a phone call or to be told on her return.
Thankfully, the bugger waited till she got home. I didn't mind the burden, but my mum said it was a horrible conversation to have before leaving her