its not worth the time. once wet and or swollen, i will fall apart.
I agree, its probably not worth trying to fix it. I would just replace it.
It really depends on how wet the substrate got, and which composite the substrate is. There are different types of "particle board". I can buy a composite called "particle board", which is actually named "Southern Industrial Board". It is very dense, and glued with very small particles. It's extremely smooth.
By contrast there is particle board of much lesser quality, called "chipboard", or "flakeboard", or "underlayment", comprised of larger wood particles. There is no comparison of the two composites. The ping pong table could have been fabricated from the best quality board, or not. I've had luck in wet/swollen SIPB to allow to dry, or force dry with an air hose, and then sand flat.
So, it depends on how wet, how swollen, and the type of board in question. Lesser quality boards may just disintegrate after getting wet. But, it's worthwhile to be informed before making a blanket statement to discard.