Argthtjtr

This might be an easy one, but i had a situation where a rogue character fought against a guard who shouted to the other guards to come and help. The rogue got a boost and wanted to trip the guard and run away.
It didn't seem like conceding, really, and it's not taken out..

Is there a way to let the character leave the conflict without having to let the NPC choose their fate?

Technically, this is conceding the conflict. If the opposition (the GM) accepts it, then the conflict ends on the player's terms. If they (you?) don't accept, then the conflict continues. Now the PC must defeat the opposition by taking them out.

The trick here is realising that taking someone out does not mean murdering or beating the crap out of them. It means somehow rendering them unable to take part in the conflict. When someone's trying to run away, this may well mean that the taken out pursuer (the guard in your example) loses track of the quarry (the rogue).

Frame the action properly and it will make more sense. The objective of the rogue is to get the f* out of there. The objective of the guards is not to let the rogue do that.

The "attack" of the rogue doesn't involve hurting the guards. The rogue "attacks" the objective of the guards by running away with Athletics. The guards may try to "defend" their objective of not letting the rogue get away by giving chase with Athletics, or pinning them down with Shoot etc. What's being attacked or defended isn't bodies, but objectives in the conflict.

If the guards are taken out, they eat dust and return empty handed. If the rogue is taken out, then she is cornered with nowhere to run.

When the hurting stops, the conflict stops.

Sounds like starting a chase contest to me! This is a completely fine thing to do if you don't have to have total narrative control of your opponents to get what you want, which in this case I'm assuming is just "get away":

Transitioning to a Contest or Challenge

You may find yourself in a conflict scene where the participants are no longer interested in or willing to harm one another, because of some change in the circumstances. If that happens, and there’s still more to resolve, you can transition straight into a contest or challenge as you need. In that case, hold off on awarding the end-of-conflict fate points and whatnot until you’ve also resolved the contest or challenge.

In an earlier example, Cynere managed to get a vault door open so the three PCs could escape an endless horde of temple guardians. They all decide to run and try to lose them.

Now, the guardians and the PCs have mutually opposing goals but can’t harm one another, so now it’s a contest. Instead of running the next exchange, Amanda just starts setting up for the chase.

Fate SRD, Conflicts

Assuming you're alone, you can break and run from combat at any time circumstances would permit. You can probably even keep the "trip and fall" boost as a penalty to the guards' first action in the chase contest, assuming they're interested in pursuing you.

Now there's just the problem of deciding stakes for the contest. "You get away clean" vs "they capture you" or "they corner you and you have to fight", maybe? Anyway, once you hash that out, you can do a quick race to 3.