usually, when the token is unsold, they will airdrop to investors or those tokens will be burn.
Burning the token which is unsolved is the better idea then others because it actually not going to touch the where you after talking even after the sale but if it airdropped to the investors or to the participants to promote more then it will decrease holding current value to further more.
Token burning has its flaws as well and depends on the utility of the project we are talking. If the project needs a reasonable supply in order to make the project work then it is wrong to burn them. I think that a combination of these 3 ways is the best. And probably you can lock some tokens for a certain period that may be unlocked for a sale or to potential investors that achieve a certain trading volume. This raises awareness of your project.