If there will be such cases ^{although am not sure if such has happened} it will only affect campaigns run using btc as payment, because when the price of btc is down it will certainly affect the allocation of the campaign, the value in usdt at the time of the campaign will be less, participants will be left with the option to hodl for a more favourable market before selling if they wish. I doubt it is enough for anyone to leave a campaign since it is a known fact that the market will recover at some point.

Campaigns run with usdt payment on the other hand don't experience this price fluctuations as usdt is known to be stablecoin.
Generally speaking, I think majority of people in crypto already past the time of irrational and regretful decision as a result of price functions.