The presence, absence, position, or style of any character on any piece of merchandise has no bearing on any future (or past) plot points. I design the merchandise to look good and sell well. Usually, I specifically design the merchandise in order to avoid any sort of plot relevance; the Thog kids shirt still has all his tusks unbroken, for example. I generally choose the most "iconic" look for each character, if there is such a thing.
In the case of Leeky, there were three reasons I chose him:
- He was shorter than Hilgya, and thus better parodied the "child" slot of the original family stickers.
- He is the only druid in the comic, and has strong appeal to people who like druids.
- He is significantly less of a pain in the ass to convert to line art than Hilgya is, due to differences in how I constructed the art way back during the first book. And I had a lot of art to make for those shirts.
I assure you that reason #3 was the biggest factor, by a fair margin.
Also, my lack of commenting on a topic does not implicitly confirm or deny the proposition being put forth. Sometimes, I just don't care enough to respond. I may be low on time and decide that something is too trivial to bother answering. Heck, the fact that I respond to things at all is a relatively recent development.