I've no plans to introduce user sumbissions. But it would be perfectly possible for you to create an 'add-on' plug-in (don't edit the plug-in directly). The next update will include a function which you can user to create events (a bit like what
wp_insert_post is for posts. You would then simply need to provide the forms etc, process the data and then call that function.
Event Organise stores dates in a seperate table which is deleted when the plug-in is (properly) uninstalled. In that sense, yes the will. However, you can export the events into an ICAL file, and then as long as the plug-in they are migrating to can import and ICAL file, you should be fine. If you do do that, make sure you make a back up of all data and run a few tests firsts. You won't want to uinstall Event Organiser only to find the other plug-in won't import them correctly.