I didn’t tear my bicep but I severely strained it using mixed-grip. It took a year to fully recover and when I did it the pain was unreal. A complete bicep tear is tougher and would require surgery within a week of doing it because the muscle will retract and surgery gets more complicated.
It happens if you flex your arms during deadlift instead of simply letting them hang. I also stopped doing bicep curls (or if I do bicep curls I’ll only do them immediately after deadlift). Fatigued muscles are much more prone to tears and strains. So curling on Tuesday and deadlifting within a couple days of that is a real bad idea.
I deadlift and continue to use a mixed grip - just much more aware of letting the arms hang and pulling slack out of the bar before lifting.
Your grip will give out easier on dual overhand grip unless you use a hook grip and that takes some getting used to. If you’re not competing in powerlifting then straps are great to use.