It's impossible to know precisely what has been damaged unless you either:
1. remove the cylinder head and look
2. replace the belt and do a compession test
Your engine is an interference fit type of engine so bent valves is a distinct possibility and you should probably assume it.
It might be possible to check for bent valves without doing #1 or #2....such as removing all the spark plugs, and just installing one plug, and then rotating the engine by hand and seeing if there is any compression in the one cylinder that still has the spark plug. This is very imprecise, but if the valve on that one cylinder is really bent badly, you will be able to spin the engine by hand without much resistance--since there is very little compression. Of course you'd have to do this for all 4 cylinders, one at a time.
Sometimes, on some engines, you can also loosen the camshaft caps, allowing the cam to move and thus insuring that all the valves are closed. Then you can shoot compressed air into each cylinder one at a time to see if there is severe leakage past the closed valves.