Do I think you need to buy a backup firearm? Not nessisarily.

However, I would at least make sure that there is one availible for you to use depending on your situation.

Ask yourself this:

If you dropped your gun from your treestand, and somehow damaged it - would you be ****acke out of luck, or would there be a gun availible for you to use within a matter of a short walk back to the ( cabin, house, farm, barn, truck, friend's truck, friend's house, ect, ect ). If there is a gun you can use, and would be confident in using, then I wouldn't worry about the purchase, and just pick up an extra gun when you can.

If you said "NO, I don't have a gun that I could use within a matter of a short walk, an hour, whatever" - then I would probably pick up an extra rifle, get it sighted in.