What would happen to your data if your software company went out of business tomorrow? Would you be able to get your information out and transfer it to a competing product?
This may not seem possible. Software companies are large, powerful, profitable companies. They will be here forever. What if you chose WordPerfect in the 80's? They were THE software to have. Now you could see them going away. What if your business runs on Informix? Now that hey are owned by a former competitor, what is the guarantee that the software will continue to be maintained?
There are two possible solutions to this, you should do both.
1) Make sure your data is in a format that is accessible by tools other than the one supplied by only one vendor. This means openly specified formats. This does not mean that you need to stop using the software that you like, just that you need to store the information in a vendor neutral format. If you like MS Word, OK, but save as HTML or RTF for the things you need to save and archive.
2) If your business depends on the information, have source code for the application. If the vendor does not maintain it, you can. If you cannot, you can hire someone who can. If it is core to your business, you need to own the software. You may think that because you bought a perpetual license that you own it, but if you have no source, it is just a rental.
Imagine, if you will, that you are a large petro-physical (oil analysis) company. You spend a LOT of money on a piece of software that analyzes graphs of information about oil wells. It does exactly what you want, does it quickly, and accurately. One little issue. It is 1989, and it runs on DOS. Years go by, and the last OS it still runs on is Windows 98. When support ends, or even more importantly, when you can no longer get hardware that the OS will run on, what happens to your software investment? What happens to your data which is in a format that only this one application reads? You have now lost not only your substantial software investment, but also your data about your business. Oil wells last longer than operating systems, so the data is still relevant to your business. There is now a casing down that well, and a pump on the top, so you can't just go back in and get the data again.
Remember, if you do not have full source, your software is just a rental. That may be OK. Businesses rent things all of the time, buildings, vehicles, even furniture. Just realize that it is a rental, and one day, you won't have it any more.