89 F-150 rear end replacement.

I am looking at purchasing an 89 F150 4X4 with a rear end problem, it needs a new pinion bearing, so the owner has removed the drive shaft and is driving it in 4WD (esssentially front wheel drive). First, can I drive it home 50+ miles at low speeds like this? And second, how much would it cost to have this repaired? Or would it be easier to replace the entire rear end?