There is also the possibility to airdrop them (not talkin about giving away a little amount of tokens to the community). To maximize the investors value, unsold tokens can be distributed to them in relation to their investment. Since the founders and the team usually get a fixed amount of tokens, this increases their relative share.

https://medium.com/@FundFantasy/unsold-tokens-keep-burn-or-airdrop-them-part-2-c2d9305f94e9

of course it decreases the value for the founders and team, which is more pronounced when only a small part of the total amount of tokens is sold. One could complicate things and implement like a linear function and make it fair for both the investor and the founders and team? Should one party be rewarded to a greater extent? The ones taking the risk in times when trust in ICOs is low? Or the founders, BECAUSE THEY ARE THE FOUNDERS?