No we cannot, it not that simple unless he retire's and even then the AFL investigate the circumstances, The Crows cannot delist a player with a current contract without reason, ie breach of contract and even then they need to jump through hoops.
Yes, they can.
However, if they choose to do so then they must pay out the salary for any remaining years, and the salary for future years is included in the current year's TPP.
For example, if a player had a $150k per year contract, with 1 year left to run... we'd have to pay them $300k this year (the 2017 & 2018 salaries), and all $300k would count against our 2017 salary cap.
** The above only holds true if the player does not end up on an AFL list the following year. If we were to re-draft him (i.e. in the Rookie Draft), then he would receive $150k in 2017 and $150k while on the rookie list in 2018. If he were drafted by another club, we'd have to pay the difference between his 2018 contract at his new club and the $150k he would have received at Adelaide.