With a high magic setting, I think things would adapt :P I could see the Elves living in giant boats of living wood, the Dwarves owning the mountains that make up the largest remaining landmasses and having a near monopoly on large ship construction, and the aquatic races becoming very powerful as suddenly everyone is forced to deal with them. Not even any reason to have tech destroyed, it would just change. Also, I could totally see there being a thriving industry among pirates of tearing apart ruined boats and combining the still intact portions to form new vessels that are a blend of old world styles. Also, I imagine that aquatic races such as Sahuagin and the merfolk would be able to construct ships from aquatic materials, then sell them to the surface races.

Ooh, also, Dwarves would probably be the leading pioneers of all-metal boats, but more commonly (and way more cool) they could build boats out of that type of volcanic stone that actually floats.

Also, I found a thing that would be cool to incorporate: http://strolen.com/viewing/Anchor_Spirits