Risk of yeast stopping before fermentation is through
 

I'm making an imperial ipa with projected Abv of 8.7. Should I be concerned about the yeast dropping out before reaching that Abv.

Anytime I go over 6% abv my concern with the yeast finishing increases. The way to deal with that concern is to pitch a sufficient quantity of healthy yeast (make a good starter), pitch it at the right temp (at or a bit below your fermentation temp), properly aerate or oxygenate the wort (for a beer of this size I use a shot of oxygen, at minimum vigorously shake it for five minutes) and manage your fermentation temp until it's finished (keep it consistent throughout active fermentation and bring it up some as activity wanes). Good luck.

pitch 2 packs of Safale S-05 and you'll be good, no concerns of it not making it

You'll get more relevant answers if you tell us what yeast you're using...

+1
In addition it definitely is relevant to know the type of yeast strain you are using and the rating of flocculation it has. I fou are using a yeast rated with high flocculation than the chances of it dropping out prematurely are greater than a low flocculating yeast and your fermentation temperatures will play into this.

For example if you ferment a high flocculating yeast at a lwer than optimal temperature than the yeast will simply drop out before finishing their task.

If you post your recipe and yeast we can assist you further with getting it pitched and fermented properly:)

I'll second the 2 packs of S-05 recommendation, I've used it to almost 10% ABV w/o issue.

also, the drill attached stir device is a cheap (~$5) way to ensure good aeration (better than stirring and rocking) without stepping up to oxygen. I also double pitch with dry ale yeast for any higher gravity ales...but a starter is the way to go if you are using liquid...youtube video instructions here.....

That may be the most unflattering vid capture ever above....

I settled in wyeast 1056