It's always very difficult to say what a person's job opportunities are. I can describe to you a general or typical situation but the world of EFL is vast. Employers are looking for teachers in a massive variety of countries, the teaching requirements vary enormously, as well as the political, cultural and economic factors. I'm also considering your situation on the basis of what you have told me about yourself, which is obviously an incomplete picture of your 61 years! The following is intended as guidance. Tefl.net cannot be held responsible for any decisions you make based on the following.
The first thing you need to do is to decide what sort of teaching you would like to do. Given your background in software engineering, you could consider posts in higher education. In-company work is another option, especially if you find an organisation in the software field. In these cases, your age and experience can work for you. On the other hand, you might want to get away from this type of work completely. If so, you can consider general EFL work which might not pay as much. You have also mentioned voluntary work in literacy. This is another option but you would need to choose a country where English is the second language (India, Singapore, etc). I suggest posting your CV on a website.
You can also consider whether you want to work for yourself on a freelance basis, hiring out your services to companies or whether you want a contract with a school. It's probably wiser to start out working for a school while you gain experience. You should also consider whether you want to work exclusively for one school or work part-time for two or three different schools. If you go for the latter, choose your destination carefully. Choose a place with a number of higher education establishments, a good business district and a number of EFL schools.
When considering an offer from a school, you can do as you have just done and post a question onto websites to get more information about it.
It is difficult to say what your realistic prospects are. Everything depends on the country you want to work in, the state of that country's economy and the type of teaching you want to do. Short-term positions are available but most employers prefer teachers who stay at least one academic year. You ask about the possibility of just walking away if the situation is intolerable. I would advise against it. I would avoid getting into such a situation by getting as much information as possible about the post beforehand. If you find that the situation is difficult, talk to your employer before it gets intolerable. If you leave giving only a short notice period, the people who suffer are usually your students and colleagues. If a situation is intolerable, it's wise to choose your moment for leaving, e.g. at the time of a school break. Give as much notice as possible. You'll probably find that once you have handed in your notice, the situation becomes more bearable.
As for healthcare, I can't really answer that. It all depends on your choice of country. This is something to look into before starting out. Get info about healthcare in the country and decide whether private cover is needed.
There are usually no problems with a spouse. You don't say whether she intends working too. It's a good idea for her to consider this. If you are working and she isn't, she could feel at a loose end. In addition to this, she'll be dealing with a new country and culture away from friends and family. It would make it easier for her to settle in if she had some work to do. She could consider working for a few hours a week or even voluntary work. The consulate of your country might be able to help with some ideas.