Did you ever stop to think that, despite this being a potential problem, why it has not been a problem?
Android isn't an immature product. google have activated something like 300 million devices. 300 million opportunities for your theoretical issue to manifest and yet it hasn't.
No, of course I didn't stop to think, that would just be a waste of my time - much better to just send off a response without any thought what so ever...
Of course, back in reality, I do actually know someone that installed Swype on their Android phone, didn't like it, and couldn't figure how to get back to the default keyboard, so I don't know why you think these types of problems aren't already cropping up in the Android world.
New keyboards have to be manually activated in Android, via the same mechanism that you'd use to switch to the default keyboard, so that honestly sounds like a pretty straightforward PEBKAC (heh) problem.
Turning on Swype implicitly trains you in how to turn it off.
Android isn't an immature product. google have activated something like 300 million devices. 300 million opportunities for your theoretical issue to manifest and yet it hasn't.