will the unsold token be burnt?
I guess,thats standard and easiest thing to do with unsold tokens.
Is there any way those tokens can be reused for something else and not burned?
Well they can and some projects have done it that way but it usually brings concern from the community as those tokens could be used in certain ways that the community disapproves of.
In cases when they decide to reuse the tokens, they are often given to investors as bonuses, but since those are free people often look down on them and sell for a lower price. This is a possible instability in the market and can cause issues for the project.
Sometimes they keep them and sell them in later stages to invest in development or something else that project needs.