Can I stay in our 55+ community?

Is the housing subsidized? That might create a problem for you.

If not, you can always have mom put you on the lease and then you are on the lease and no subject to eviction because the leaseholder is no longer living.

Since ur so close to 55 I don't see why they wouldn't allow u to stay. As long as the rent was paid on time, the place kept clean and you have not been a problem I don't see a problem. But that is a question for your landlord.

Firstly I believe that it is unlikely that "failure to do therapy" will make your Mom's death imminent. The more likely screnario, unless she has cancer (in which case therapy will do nothing) is that she will go on, debilitated, to a long slow slide. I think you cannot predict how long this will take.
I cannot imagine, to be frank, a company that would kick you out for this several months time, but then I don't know the management where you are living, so there IS that. Just occasionally we hear of people buying into something where they long to get rid of them so that they can get someone ELSE to buy in at newer and higher rates.
Do know, as well, if you absolutely MUST know, then a lawyer who specializes in rental and housing could likely answer, or another community you go to to explore, ask them about that possibility.
I am assuming this is a decent place with decent management. IF something happens to Mom I would simply handle all the after effects of that, saying nothing to the management, and if they come to you, saying that it is something you never even has a second to consider (yes. I can lie if I think I have to, hee hee especially survival, and housing, shelter, falls under Maslow's hierarchy of needs in the top three, along with food).
OR the other option, with a decent management, is to go and be scrupulously honest, telling then of the only several months lapse.
It is up to you how you handle it, but try now, in the midst of all the severe trauma you are going through, simple to get through this a day at a time, trying not to hystericalize what may be coming down the pike at you. I have a tendency to do that myself, and can take it all the way to the possibility of exploding hot water heater tanks. Which kind of adds to the trauma of what I am going through that day for no good reason, if you get my meaning.
Wishing you the very best and hoping you will update us.

Do you have a lease? If so, review it. Otherwise, call the office and ask them the details. I would hope that even if there is a rule against it, that they would not throw you out when you are so close to the cutoff.

Perhaps mom will rally and you won't have to worry about it!