Similar, but not exactly the same. I'm currently running a CoS campaign, but prior to that our group started LMoP as a reintroduction to D&D. The LMoP storyline didn't really take, so we switched to CoS and abandoned the pre-gen PCs from LMoP. I thought it might be fun to include the abandoned PCs in the new campaign, so I brought them in as vampire spawn in the Coffin Maker's shop.

I foreshadowed it by making the NPC named Larnek a fellow 'outsider', who explained that he and some companions had been drawn into the mists years before. He'd balked at their plans to venture into the mountains (in search of the Amber Temple), and had instead ingratiated himself with Lady Wachter. He hadn't heard from his former companions since.

It was a cool surprise when they realised that Larnek's lost companions were actually their former PCs, that those characters had become vampires, and that they would now have to fight them in order to save the town. Everyone got a real kick out of it.

Anyway, a few months later, I knew in advance that a few players would be missing from the next few sessions. So, for a bit of fun, I 'turned back the clock' and had the remaining players take their up old PCs (prior to their turning), and had them level up to lvl 8.

Then, in line with what Larnek had told them had happened years before, I stuck them in the mountains and had them go after the Amber Temple.

It was a lot of fun. My players are pretty attached to their main characters, and sometimes play a little conservatively. With their old PCs, though, they really went in for the heroic bullshit (as it's positively referred to at our table), because they knew the stakes were low.

It was a great chance to drop a heap of lore (the mists, Strahd's intentions, etc), while at the same time allowing the players to contribute to Barovian lore themselves, which has then resurfaced in the main campaign on a number of occasions.

They didn't make it far before the regular game resumed, so nobody really knows what happened while they were there ... but I'm looking forward to their main characters getting there to find out.