While I disagree with much of what Johnny wrote above, I do agree that WebOS may not be the limiting factor for Palm Pre sales.
There is little, other than elbow grease, that would prevent a WebOS-compatible container being written for Android. It might not even require firmware changes. I sorta expected somebody to have already written a WebOS-alike framework for Android or iPhone or something else with WebKit baked in. There might need to be firmware changes to address a small percentage of WebOS features that lack Android analogues, but most core stuff should work OK AFAICT.
The Pre has a faster CPU than many of the early crop of Android devices, but the next wave, starting with the Motorola DROID, should have plenty of horsepower to run a WebKit-based app fluidly. The DROID, for example, has the same CPU as the Pre, IIRC.
So, if Palm did decide to go with Android, they would "merely" have to write a WebOS container for Android, then they could carry over all their existing WebOS apps, yet still have access to Android apps.
Conversely, should Palm kick the bucket or head seriously in that direction, the WebOS community could work to create such a container so they could continue their app development. As PhoneGap and Appcelerator Titanium Mobile have demonstrated, it is very possible to create cross-platform mobile apps using WebKit, so a WebOS container could be written that ran on multiple mobile platforms.