Long story short, my driveshaft came off the other night while I was on the highway going about 70. It shattered my tail end of my transmission housing and now I found a crack on the inside. What to do? I found the tail end of the housing for $60, but I have no clue what to do about the crack on the inside. I need it gone, it was actually for sale when this happened.

 

need some more information.. what year truck? what engine? what transmission?

From the pictures you posted, its difficult to see what the damage is, but I assume this is a 4R70/4R75 and the rear of the case is cracked where the output shaft comes out.

you will need to replace the transmission case or just replace the transmission.