Slitherine

In real life, surviving regiments of the 106th Inf. Div. escaped Schoenberg and along with the 112th regiment of the 28th Inf. Div., staged a heroic defense of St. Vith that held against overwhelming German forces until the 21st of December.

is this possible in the game ( with some very unlucky rolls for the German player?) or is Kurt Vonnegut's 106th totally doomed? can St Vith be held by the Americans until the 21st?

Never have seen it, unfortunately... no "fortified goose egg" here.

I have seen the 101st Airborne wind up in and assist in the heroic defense of Bastogne a couple of times, though.

That's something that did trouble me a bit during development. I finally rationalized it this way: the counters represent divisions as a cohesive fighting unit, and by that standard I think you can argue the 106th was effectively destroyed within a few days of the battle's start. Surviving units being used to stiffen up other units is abstracted under the Replacements mechanic.

I have seen the Allies hold St. Vith a few times in playtesting, but rarely for as long as it held historically. Even if the Germans don't manage to take it the first day, they can usually make the position untenable pretty quickly.

Very rarely I’ve seen 106 Inf get rescued (at least back into supply).

I've seen it done too, but the usual result is that you lose both the 106th and the luckless unit chosen to rescue them (usually the 99th).