I think it won't shorten the life of the sensor. I think condensation build up could be an issue, so I would say if this is an aftermarket wideband sensor just give it time to warm up before starting the car. I think I would be more worried about the alternator and things in the surrounding area getting blasted with hot exhaust gas .

Damn, you ran with JUST an o2 housing on for a year? I cant believe nothing melted.... Thats amazing
I would never run exhaust gas that close to the fans/radiator/alternator
Cant you just pick up an old down pipe and, IDK, find a way to mount it? I mean even drilling a hole through it and running some wire as a temp rear support?? Theres gotta be a way dude, you need a down pipe

Over a year actually. It's really not as bad as it seems, its diverted far enough out the engine bay to not really affect anything as far as I can tell. I forgot to mention another downside, my trans and some of the oil pan are really dirty from the exhaust being that close. Alternator and everything held up great though (although I have a lifetime warrenty on the alt so not worried about it either way).

Like I said in my op though I have a downpipe and I have one on at the moment (the stock one). But the vibration it causes is terrible. With the combination of that, prothane mm inserts and my balance shafts removed the vibration/ride-ability is ridiculous (and this is coming from someone that ran no downpipe for over a year)

I'm just worried if I take the downpipe off is my o2 sensor going to die in a week or two.

Well, its not that your o2 will die, the problem lies in how ACCURATE it will be. My dsm is at paint/body shop now or id go check but im pretty sure theres not more than a couple inches past the o2 where the housing ends. The only thing i could think of is that it may run a bit on the rich side if ambient air gets drafted up that housing a little. It might make it read lean and the ecu will compensate, ya know?
I have heard of this happening before in another thread. Cant remember, its been awhile.

I think the longevity of the sensor would not be affected though.