The FBI originally thought he jumped around Lake Merwin. That's where their search was conducted. The terrain in the drop-zone there is very rugged, and the chance of a bad landing is very likely.
The pilots later said that he jumped over the northern suburbs of Portland/Vancouver. They claimed that this is where they were when they felt the bump of the tail-door snapping back up after Cooper's weight was removed from it. The drop-zone here would be either urban, or (much more likely) farm land. Probably still a bit of a hike, but not as bad as 'wilderness'.
I think he must have survived. Granted, he took the worst parachute; but it was still a serviceable one. And given the drop-zone based on the pilots recollection, if he had perished someone surely must have found him by now.
The last reason is that if he had perished, either in the wilderness that the FBI was searching, or in a neglected bit of the later drop-zone, it is highly unlikely that the three bundles of money could have ended up where they did without someone moving them later. Firstly because (with the exception of Lacamas Creek) the watersheds don't move things that way (Clark County has a very good map of all its watersheds). Secondly, the flooding and dredging histories of the Columbia river make it unlikely that the money was in the water all that time.
That's just my 2 cents