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 because each succeeding generation are bigger snowflakes. And, get off my lawn!
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