Not sure why a "Safari crash" would impact Aperture.
I'll try to offer some suggestions.
On the iMac, go into your home/preferences and locate
library/preferences/com.apple.aperture.plist
Move this file to the trash.
Now, REBOOT the iMac.
When you get back to the finder, EMPTY the trash.
Can you now open Aperture (yes, you'll have to re-set some things)?
Something else I would try:
This assumes the iMac still boots and runs ok.
BE AWARE that SOME 3tb iMacs (from 2012-13) have had defective 3tb hard drives. Could some sectors of your drive be "going bad" on you?
In any case:
You will need an external drive, 1tb or larger. It has to be able to hold the entire Aperture library.
I would next download CarbonCopyCloner from here:
http://www.bombich.com/download.html
CCC is FREE to download and use for 30 days.
Doing this costs you nothing.
Now... open CCC
Put your source (the internal 3tb drive) on the left.
Put your target (the external drive) in "the center spot".
Now... look in CCC's window to the left/center.
See "all files"?
Change that to "some files".
Now, you need to UNCHECK EVERYTHING with ONE EXCEPTION:
users/home/pictures/aperture library
This is the ONLY thing that should remain checked.
Now, turn CCC lose and let it clone ONLY the Aperture library to the external drive.
WHY you want to do this (instead of doing it with TM or the finder):
If the finder tries to copy a folder, and if it encounters even one "bad file", the ENTIRE copy process will be aborted.
I don't know how TM behaves, I refuse to touch it.
But with CCC, if it encounters one or more bad files during a clone, IT DOESN'T STOP the process. Instead, it makes note of the bad file(s) and keeps right on going.
What you end up with is a cloned backup with "all the good files", and a list of the files that wouldn't copy.
With as library of 800gb (I think this should have been "broken up", but too late now), there's almost certainly going to be some bad files in there somewhere.
If you do this, you should have "in hand" a "good copy" of the Aperture library as it exists on the iMac.
You -might- be able to open this on the MBP.
One other thing:
It's time to upgrade beyond Yosemite.
I'd suggest at least El Capitan, perhaps Low Sierra.