It’s a good question to consider before you buy software. What happens if the vendor goes under? What happens if they release a new version and stop supporting the old one?
Here’s a good example of a small IT staff that had to deal with this very problem. The vendor had stopped supporting their order entry system, leaving them with unmaintainable software. What did they do? They fixed the problem and ensured it wouldn’t happen again. You can read the whole story right here.