Hi there,
There shouldn't be an issue once you switch if you de-register your number from iMessage first. The problem is that iMessage and SMS/MMS are two different things, and when iDevices message a number that is registered in iMessage, that's the route they go with. But if you already switched to a phone without iMessage access (aka non-iDevice), then the message just never reaches you unless your contacts specifically switch your contact to use SMS/MMS for all communications.
Unfortunately, I can't say that this will work flawlessly and painlessly as some users, even after de-registering, have issues. Some don't do anything and they don't have issues at all. It's a problem with Apple and iMessage, but one that unfortunately impacts the experience of people who have switched, which makes them blame the device/system they switch to rather than the actual source of the problem.
Just remember, if you switch, things will be different when it comes to messaging. A group in iMessage will be converted to an MMS group (lower file size limits, will only work on mobile data, etc.) when one of the recepients is a non-iMessage user. Any conversations you've had in iMessage will not be ported.