The IMG as a whole don't particularly care about the fate of escaped slaves, hence why we mention volunteers. However, those who have a more pragmatic approach may decide to use their assistance to secure some kind of favor from Crayter. Maybe they want them to resist Liberty expansion into Coronado, maybe they want increased security guarantees in the Taus from them. Now, it's also true that some IMG captains will do this job to screw with the Outcasts, regardless of the ultimate outcome. There's plenty of bad blood between them.
All this to say that the IMG will not have their own drop-off. And for those who care about the slaves, going to Yuma is still the best bet, since that's where new infrastructure is being created. Pecos just had a refugee crisis, they don't want another one.
RP during the event and RP before & after the event are categorically different. During the event, yes, you have little time to talk things out. But there's nothing stopping you from doing so. Just as with a regular pirate interaction, you have 5-10 minutes of RP, after which you are let go, or you get attacked. However, I did notice a problem that people may run into, which will be solved with a increased slave purchase timer. That being, if you get pirated, you are screwed. Now, you can go back and buy another load if you dare.
After the event, the RP which can take place isn't timed. You have plenty of opportunity to take the slaves somewhere else, embellish your experience as part of the convoy, talk about how the slaves are settling in at the various destinations, etc. This is partly why I don't want to provide a template. Take a look at The Dig and The Gala. I consider both to be very good examples of collaborative storytelling centered on an event. And the requirements for them were pretty minimal.
Now the last point about events as a whole. Anyone can make unofficial ones that center on something other than a football match of two even fleets. If people need incentives beyond the rp itself, there are many in the community swimming in cash and gear. I personally can only do so much with my other responsibilities in and out of disco. If I could drop those to focus solely on events, you could maybe see weekly mini-events, but it wouldn't be fun for me and likely burn me out. More event devs would be welcome to get closer to this point, but if you don't want to organize unofficial events, you probably wouldn't enjoy doing official ones either.