FIL has been in and out of hospital for two months. We have a 4 week overseas trip planned and paid for. Do we still go?

If this bout of ill health is outside the normal pattern for him, and depending on what his doctors say, I think I'd find out if you can postpone the trip until he's more stable and you have some clarity on his prognosis. Are you insured? Is the trip booked with a tour operator or have you planned it independently?

Not to make bones about it - how would you (or more to the point, your husband) feel if you had just got to your destination and then received the news that he had passed away?

I would go. Get travel insurance. You're already getting care for when you're not there, so do it. With no guilt. It's a little tricky, but you can't just sit around waiting for "something" to happen.

Enjoy!

Personally I would go. I am assuming with a parent this age you and your husband are of an age to be spending some quality time traveling before you yourselves will not wish to go far from home. Anything could happen to FIL while you are gone, but you have insured that someone is there. Anything could happen to him at age 92, 93, 94 and 95, a typically our elders can now live this long. Go while the going is good.