If you don’t have an exit plan, you are basically saying that you accept the risk of losing the data that is with that provider, and the capability to use that data. At its most basic, an exit plan describes how your most valuable data is stored in a secondary place. For example, my Gmail mail archive is also stored on my laptop as it is automatically downloaded by Outlook, my mail program. I have not spent too much time thinking about changing my mail provider. However, because my mail and contacts are safely stored elsewhere, I am confident that a new provider will help me to do the migration and that the process will be fairly simple.
For my customer management system I make regular copies of the entire customer database and contact details. Again, moving to a different provider will be a hassle, but not impossible. If your business really depends on it, you may want to have a cloud system on hot standby. However, most of the time, this is not very easy with SaaS because no two SaaS providers are alike. You are better off to first think about which data to save to a secure location. If and when you want to move, your functional requirements will have changed anyway, and there are likely to be new SaaS providers at that time as well.