There are still tickets for sale and showing some availability on seatcounter in Coach and First. You will be fine. The only seats to select now are preferred seats however at the gate they will assign you a seat. Safe travels.

On the 2nd part, your exit seat on the MD-88 should not be taken away. However on Delta, seats are NEVER guaranteed and they have the right to change them.

What fare class was this booked in?