As this will be my first post in roll 20, I hope this helps. I was in the exact situation you are in. I had a group of 3 people who I was DMing and they wanted to continue playing while we had just started a homebrew campaign. I worked 40+ hours a week over night so it was getting harder to create content for me at the time and still is. I talked to them about it before hand and we agreed to move over to the Tomb of Annihilation. I bought the module here and I have to tell you, it saved me more stress than I could have imagined. However, there were issues that arose. The main one being, the freedom of the group. The campaign is dangerous. People have a high chance of dying and as per the rules of Tomb of Annihilation, they are permanently dead. After a simple encounter, a wraith sneak attack round, crit with its life drain to instantly kill a party member. That domino effect caused a TPK that forced a soft reset on the campaign. Now in the reality of the campaign, the players realized, they would have to decide whether they wanted to restart, continue as new players, (which I recommend and the book suggests as well), and I decided on a soft reset. I don't want to rant before I give you more of what you want to hear. This is important because though all of this was easily facilitated by the module, how to reset on a TPK, experience and communication with the group can solve this, but a concern that rose up that we could not avoid, was something unique to this campaign. There is a time frame. There is a set destination that needs to be discovered. They cannot leave, and return. This adventure, is about stopping a world ending event, the death curse will have major rammifications if not stopped. So there is a lot of pressure to push the players into moving forward. They took a toll when people realized, they wanted to do something else. But as per the adventure, leaving Chult, is basically, choosing to throw out the entire purchase. There are no maps outside of this adventure world of Chult, and the Tomb of Annihilation. You are headed here and discovering a hex grid together, in pursuit of the Tomb. If your players decide, this isn't what we want, there can be a big whole now in your pocket, in terms of a purchased campaign, that has little flexibility, outside the plot. Now, we solved this through communication. I think for you, it will be good to discuss what would happen if there was a TPK. Because it can happen, and characters well developed that fall with the entire party, can leave a taste in peoples mouth, that ends a campaign. There are solutions in the book. That I came up with. That you will see as things develop. But I wish for me, doing what you did, I discussed this ahead of time thoroughly, because though we resolved it and continued by skipping chapters they completed already, there was a break where I felt I made the wrong choice. As for specifically, running ToA with 3 people, it is doable, and I recommend two things. 1) Creating an NPC that the players choose as their ringer to adventure with them. Discuss what they need or are looking for in terms of combat and character. They chose a druid focused on CC and tanking as a dinosaur. 2) Focus on the unique encounters ToA offers, that are not combat oriented. There will be a lot of damage rolls going on. You do not need to add to it. There is a fog that spreads madness, I made it much like the show Lost, where is crept toward them, and then chased them in a direction they did not want to head in. Discovering caches of lore, like a priest who died long ago, clutching scrolls. However, his body is dangling in the canopy above a tar pit. These two things made ToA easier for a smaller group who could be more prepared for difficult encounters designed for high risk. I hope I gave you something you can use to make your decision. Good luck!
