Would having the delay after the cab sim ruin it? No
Would it sound different if the delay was in the effects loop? It depends.
It depends on what kind of delay you are using and how it is changing the audio besides the actual delay portion. The power amp and speaker (or cab sim) in a guitar amp are kinda like an effect, sort of like a fixed EQ and compressor. And the order of effects usually matters.
When you hear delay on a record, it usually has one of two overall kinds of sound quality. Sometimes, especially on recording from the 60s and 70s, the delay is part of the guitar signal chain and it usually sounds a bit grittier. The guitar sound was delayed before going through the amp and then that sound was recorded. Any panning or EQ or other processing done during mixing tends to make the delay sound like part of the guitar tone and less like there's a canyon behind the guitarist echoing what they play. The other sound became more prevalent through the 70s as multitrack recording and mixing became more powerful. This is delay added by the engineer after the microphone has picked up the amp sound either during the recording or mixing stage. This kind of delay usually sounds cleaner and clearer and the repeats can be panned, EQed and otherwise processed separately from the main guitar sound, creating more of a distinction between the delay and the guitar tone.
If you put the delay after the cab sim, it can sound more like a studio delay, which certainly can be a good thing depending on what you're going for.
Effect order tends to be personal and also part of each players style and sound. Do it the way that feels good to you and don't worry about what other people think.