I hate to post a comment about a failed summit, but perhaps this information will be useful to other "moderate" climbers who get lured onto this route and need to find a way out (as we did).
First of all, everything you read about this route is true, but not sufficient! You should know that the "third class" terrain beyond the crux (the four aces and the "headwall") contains quite a lot of fourth class climbing with big exposure. You should also know that this "third class" portion of the ridge is VERY LONG. If you are a moderate climber who likes a rope on exposed 4th class moves, you will spend several hours on this ridge AFTER passing the moderate 5th class climbing on the aces and headwall. If you (and/or your partner) are average moderate climbers, get a permit for Ypsilon Lake and plan on spending a few days. This route in a day from the trailhead is only for soloists or mutants. (My partner and I started at 3AM from the trailhead, we were on the ridge by 7AM, we finished the aces and headwall by 11AM. At 5PM we were still flailing up the "third class" remainder, well below the summit!)
All of the "standard" exits from this climb involve passing over the summit. If you don't reach the summit, forget about finding the trail to Old Fall River Road. Forget about reaching the col between Ypsilon and Chiquita. Forget about descending Donner Ridge. There are some steep ridges that flank this mountain from the summit to the north and east that effectively cut off any hope of traversing "around the back" to the described descent routes.
Fortunately, it IS possible to bail from this route before the summit. However, it involves almost as much time and effort as going up, so be prepared to spend the night! (Much safer to bivi than stagger down the talus, snow and scree in the dark). Retreat off the north-east side of Blitzen Ridge. If you are near the summit, you can make a moderate descending traverse to the north on scree. If you are further back on the ridge, you will probably have to rappel. There are many snow filled couloirs on this side of Blitzen - they are too steep to descend. Be careful. This retreat will deposit you in the broad, shallow cirque between Ypsilon (to the west) and Fairchild (to the north). There is a gentle tongue of tundra that bisects the upper portion of this cirque, and the easiest path is to its left (north side) on the way down. Beyond that tundra covered spit of land, work back to the south (right) along the bottom of the drainage that follows the northeast side of Blitzen Ridge. (Some maps list the pools in this drainage as the "Fay Lakes".) As you curve around the "backside" of Blitzen, you will eventually see the tree covered, moderately angled slope at the end of the ridge, which will get you back to Ypsilon Lake on its south side! When we used this escape in late June 2008, there was lots of snow in this drainage, and we could glissade easily and quickly over most of it. I don't know what's under all that snow, but even if it's just scree, the angle is low enough to make a reasonable descent with no significant cliffs. An ice axe is highly recommended (also having a water filter was very helpful!).
The climbing on the aces and especially on the "headwall" was picture perfect, some of the nicest in the park. I'm glad I got to lead it, but I won't be back to "tag" this summit - guess I'm getting old!
Thank you for commenting on a this. For such an exposed and secluded climb, it's very important to have information on a descent before the summit- something that I overlooked. I added your piece to the page. Glad you made it off safely!!