No I would not do it. If Miami goes 0-6, I would bench Jake Long for the season so he can properly heal (its obvious he isnt completely healthy yet). With the, say, #8 pick...I would draft another QB like Barkley and use the #8 pick in the 2nd round to get an RT.
I like Luck just as much as anyone else, but he is a college QB. Nobody knows how he will pan out in the NFL. Top college QBs go into the NFL and do nothing sometimes. Miami drafted Pat White, Chad Henne and John Beck and well, look how that went. We need proper coaching, an OL to protect Luck.
No, you keep Long, you draft the 2nd best QB, and then use the 2nd rounder to get an RT. If you by any chance trade Marshall for a 2nd rounder, you use the other 2nd rounder to draft an OG to replace Incognito or Carey.