Businesses will take a variety of measures. The 80% (up to £2,500 per month) will apply if they choose to "furlough" you. This will mean that you can't work at all for them during that period. They may elect to top up your wages to 100%, but most will not. The trouble is that the HMRC system is not yet up and running. It may not be until the end of April.
Another option is to put you on a zero hours contract/short-time working/lay you off. Of course, this can only be done without your consent if there is a provision in your contract of employment which permits it. If there is no such provision, the business may say that it needs you to consent if you are to have any job to go back to at all.
Bear in mind that if the contract does permit short-time working/temporary lay-offs, you are entitled to redundancy if it continues for a consecutive period of 4 weeks or for six weeks in any 13-week period.
Unfortunately, some businesses will not survive this. If a business enters into administration or similar, your redundancy claim will rank quite far down the list (after secured debts such as loans, by way of example).
Your DH will unfortunately be a prime target for dismissal owing to his length of service.
It might be worth asking if they will furlough you.