I used to be an 'accident reconstruction expert' before I retired several years ago.
When it comes to a criminal investigation - unfortunately a 'death' (accidentally running over a bicylicst, etc) ranks pretty low, usually just a misdemeanor manslaughter unless there is some sort of gross negligence involved
Now when it comes to a repeat DUI offenders that causes a fatal accident - that is a different story, and they would probable be looking at 2nd degree murder charge.
Where I worked, any serious injury, fatal or major felony would result in the immediate seizure of all the involved vehicles for a comprehensive mechanical inspection. If charges were filed, the vehicles (and their contents) would be held as evidence - until the trial concluded, which would usually take over a year. Only authorized personnel touched the vehicle once the police were on the scene.
If I found out that someone had deliberately removed a dash cam before we got there and didn't say anything about it - well, that would almost be like Tom Brady and his cell phone
A personal injury suit - is where they would rake you over the coals
Fenderman - you must live in the sticks somewhere, because this is pretty much standard procedure - especially in S Cal