What size tank is it? We used to have a 30 gallon particle board stand on our old saltwater tank... That thing probably got a good bit of water on it - never flooded, but it got it's share of water, and the only reason I'm not using it now (I'm just now in the process of setting it back up) is because its like 20 years old. I don't trust particle board stands even though ours lasted - i'm going to spend the extra money and get a pine, maybe oak stand.
Back to your question, I don't know how many times this can happen, it just lowers the stability a little each time. You can probably tell how much damage has been done by just looking at it and seeing if it is bowing or anything. Sorry for not being able to help much - my 2 cents