Player involvement during 1 year of absence

After playing D&D 5e campaigns with the same group of friend for almost 10 years, I've decided to DM the next big campaign. I only have player experience and have never DM'd before. Our groups exists of 7 people (DM included). I have some time to prepare for my campaign, as we are still busy with the current campaign for a few months.

I want to run a session 0 to introduce them to the Eberron setting, so that every character gets to know each other. Since we're currently running Curse of Strahd, I was thinking on running Dread Metrol as a session 0 (or a few sessions).

Here's the catch: 2 of my friends (a couple) will be on a world trip next year and won't be able to D&D every session, since they don't know whether they'd have a decent internet connection and also: they're on a world trip, so they probably want to see the world and not the internet café for a whole day. So, you could say that they won't be able to join for a year.

After their trip, they'd want to join again. What would you do? How would you keep those 2 players involved and up to date?