D&D and RPG's in general usually require two things: Number one, a DM to run the game, and number two a party of 3-6 players to participate in the game. I have played RPG's for almost two decades now and have run or been a member of numerous campaigns. Inevitably, life will always get in the way at some point and either the DM or too many party members will be missing to continue the campaign. Here are a few things you can do if you have too many people missing to continue your campaign.
In recent years, tons of modular games have come out, and these are great substitutions if you can’t get your group together. Modular games, for those of you who don’t know, are games where you either play through a scenario in the rule book that will require specific game pieces, game pieces where as a party you play against the board, or another player who will be controlling all the monsters for that game.
Great examples of these are the D&D branded games, the Zombicide series, Mice and Mystics, and the World of Smog. The list goes on and on. In the D&D games, Zombicide, and Mice and Mystics, players will all have unique characters to explore the map and fight monsters which will move in predetermined fashion, since there is no one specifically controlling them. As you progress though these games you will gain experience and equipment and all the things you would do in RPGs.
In games such as World of Smog, and others like it, one player will be what is usually referred to as the nemesis and be in charge of all the big bad monsters you will encounter through the course of the game. This is the traditional role of the DM.
If you don’t feel like playing something modular, you can always play one of the games that has a raid like mechanic. In these games your group will not be exploring the dungeon, you’re just skipping right to “punching the boss in the face” part of the game. As a group you will all have unique characters and classes, and team up to fight a singular over powered boss. Some examples of these games are Sentinels of the Multiverse, or Cutthroat Caverns.
There you have it. Some easy board game replacements should life get in the way of your group meet ups and you still need your RPG fix.
--Saul, "Better Call"--