I had memorized Summon Armoured Undead Decapitator. Then I respec'd. Now I've attempted around 80 times to craft a scroll of it with 3, 4, and 5 crafting. No luck. Same spells over and over and over, which leads me to believe this spell isn't craftable at all. Because I used my found skillbook (or scroll I turned into a skillbook, can't remember), am I doomed to never cast this spell again? Merchants in Cyseal and Silverglen seem to always have the same spells.

I'm level 15... Is there another merchant I currently have access to that I can check that I just haven't remembered?

I've read that there are "one-time" spells that can be lost on respec, maybe this is one of them.

That would be remarkable if true as I'm sure it's not an intended punishment. There's no reason this one would be left out of the crafting repertoire except by accident. I thought I would be safe waiting to play this game a full year after buying it, but I'm finding it's as polished and unbalanced as a beta.

I can't say I disagree completely. I feel it's a really great game but definitely has some pestering minor bugs. My biggest complaint is when the cursor gets "jammed" when clicking between inventory categories -- when one page is much much longer than the next and the cursor gets stuck in empty inventory.

I think there are only one or two unique spells that can be lost in respec. I'm playing as a purist on my first run (which isn't quite complete) so I haven't played around with respec, thus I can't confirm this 100%.

I crafted a skillbook from a random scroll before I found the placed book .
AFAIK Any skillbook you find placed outside of a container is a 1 timer. Summon Wolf also springs to mind (but again you can make a book from a found scroll)
There's always a chance you'll get a scroll from a random drop or random merchant inventory shuffle on level up.

I haven't messed around much with crafting random scrolls (I did it once hoping for a master geomancy scroll and got bless), but I was able to craft the skillbook by finding a scroll for it on a merchant (in my case, the enchantress in Cyseal square).

I'd look around at all the magically inclined vendors you have access to. You can also get lucky with a chest/barrel/etc, that's how I got the scroll to craft my Earthquake book.

I've crafted Summon Armoured Undead Decapitator scrolls plenty of times. It's how I get that skill as early as possible.