Sometimes a large battle or a battle in a complex environment can just be too complex for me to run in TotM, but there are compromises that can be made between TotM and getting back on the grid.
Sometimes I'll use a whiteboard with no grid that I can draw on to represent walls, obstacles, and areas of cover and/or darkness, etc. It's not a scale drawing, just an approximation. We use tokens or miniatures to represent the approximate location of the combatants. Explain to the Players that the map and counters are just an aid to help keep track of all the details involved - who attacking whom, whose taking cover behind those pillars, or who's in that dimly lit area in the corner, but not a scale representation of the actual battlefield.
Another idea is simply to draw circles on the whiteboard that represent areas and objects in the environment such as "behind cover", "on ridge above the rest of the players" or "chest" for the player trying to break into it while the others do battle. Have the players put their tokens in the circle that applies to them based on the descriptions of the combat. Players can also group their tokens or minis around their opponents to indicate who their fighting instead of representing their physical location or orientation to their enemy. Reach, distances and things like grouping will still need to be described in TotM.
I wouldn't do this for every combat, but if you have a lot going on these compromises really might help everyone at the table to stop trying to keep up with all the details and concentrate on using good descriptions of the combat.