Being able to rally however many players you want on-demand for any map you want to play on without the players saying "no" to it is a dream come true, and it's a good form of training at any rate that requires a different set of approaches and strategies to optimize your scores. It's enough to warrant competing with other humans for botmatch scores within different parameters, in addition to competing against people directly in netgames. There are of course some limits that we may overcome someday, such as not having different randomized color tables for the same weapon class, or the bots not being affected by liquid velocity. I've also done some personal modification to make bots drop their weapons upon death, since sometimes in netmaps (especially in the older netmaps) you can have an instance where there's only a little weaponry in a remote or hidden spot and you're forced to eat shit over and over because that causes bots to spawn already with that weaponry. Overall, however, this is a revolutionary invention for Marathon gaming that opens up many doors and allows an experience that even human deathmatch can't completely reach (though the same is also true in reverse). Take a look at the Lua script sometime, it's educational.
Single Player Network Game is a set of Lua, physics, and shapes to simulate a network game using bots. The lua script automatically populates maps with the bot monsters, and the shapes and physics make them look and act like players in a multiplayer game. Note that this only works on netmaps that don't have embedded physics (this is the vast majority of netmaps). There are many configurable settings you can tweak to get just the multiplayer experience you're looking for.
This project is based on RadBurn's Marathon Conflict mod, and wouldn't exist without the work he put in to create the shapes and the original set of physics. I've included the unmodified Conflict shapes in this download to simplify the setup process, but RadBurn did all of the work for that. I have tweaked the physics a bit from the original conflict physics, mostly to make the bots act more like real players in a network game.
If you're just wanting to be able to revive in a single player game without reloading the map/saved game, then there's also a script for that that doesn't have any of the bot stuff.
Adminn said he'd make this script, but it's been literally forever and he hasn't done it.
(Requires Alephone v1.4)