Sorry, another complicated question about triggering and resolving. At least it doesn't involve Band of Misfits or Inheritance.
I'm wondering if I'm understanding this correctly.
1) I have Innovation and Capitalism. With Haggler in play, buy Mint. When-buys for Haggler and Mint trigger.
Haggler: Gain&play Merchant Guild (cost-reduced).
When-buy for Merchant Guild triggers (for buying Mint).
Mint: Trash Treasures, including Merchant Guild.
Merchant Guild: +1 Coffers.
(The Merchant Guild was not in play originally, and not in play when I resolve it, but it triggered.)
2) I have Innovation. With Haggler in play, buy Lab. When-buy for Haggler triggers.
Haggler: Gain&play Procession, playing Merchant Guild from hand (trashing the Merchant Guild).
When-buy for Merchant Guild doesn't trigger (for buying Lab), since it's not in play anymore.
The difference is that in (2), the Merchant Guild is not in play after we have resolved a when-play ability and we're checking for more.
I'm not sure if this is how it's intended to work, but this is my assumption.