D&D 5e combat is low stakes
At least, in the sense that anyone is at serious risk of dying in any given combat. Each edition of D&D has progressively made dying less likely.
However, perceptions of risk can vary greatly from one side of the DMs screen to the other. Remember, you have a lot of information that the players don’t; what looks like a cakewalk to you may seem like a life-and-death struggle to them. And, more rarely, vice-versa.
If the dramatic question your combat poses is “Will the PCs die?” The answer is almost invariably “No”. The game is biased towards the players, and not in the way a paid off referee in a football match is; more in the way a Soviet show trial is biased towards the state. In fact, the encounter design in the DMG assumes players never use limited resources (except HP); the rating of an encounter is based on using weapon attacks and cantrips alone.
So, don’t ask that question.
Instead, ask questions like:
- Can the players end the combat in time to stop the ritual?
- ... before the prisoner gets executed?
- ... before the alarm Is raised?
- ... before the guard captain recognizes them?
- ... with enough resources left to push further into the dungeon?
- etc
