Health is far more important than money of course. But, with the huge userbase of TM, people willing to pay for an upgrade to TM2 or at least some added features (I've some too), would it be an idea for you to hire someone else to ease the workload a bit? I know from experience it's very difficult to get someone else involved. After all, it's your program, you've invensted so much time in it. It's almost your child. But children grow up, become teenager and eventually even adults. This is the line software generally follows as well. What's the moment to distantiate a bit from that child / software? Well, if health issues start to influence the health of the product, it's becoming time to find solutions to keep the software ahead of the competition.
One way is to get other programmers to do work for you. You probably have skilled friends who can be of service here. I'd guess you'll find enough people here willing to pay in advance.
Anyway, stopping the development because of health issues is understandable from a personal point of view and should be respected IMO. But it does interfere with the TM software development itself and it does interfere with everyone using TM every day, like me. If one day another editor does fulfill my wishes better than TM I'd hesistate not a moment and just move over to the other program - my work also has to continue and if I can do it a bit quicker, it's probably worth the investmen. I don't mind if the costs are $10 or $100.