Mirrors rarely (read: never) break through normal usage; the main advantage of mirrorless is not having to accommodate the mirror box which means cameras can be smaller.
Want to increase battery life? Build a bigger battery. Want to protect the sensor? Build a mechanism to cover it when changing lenses.
Is there actually a technical reason you can't make a mirrorless as good as a DSLR?
There are tradeoffs that a DSLR makes to provide a through the lens optical viewfinder and phase detection autofocus. Mechanical complexity of a moving mirror and the bulk of a pentaprism in addition to the mirror bulk are among them. For some applications and some people the tradeoff is worth it for others it isn't.
If smaller size and lighter weight are more important then a mirrorless is more likely to be better.
If the reason for getting rid of the mirror is mechanical reliability I don't think it's a good idea to add something else that can break.
There isn't a technical reason, but rather which trade offs do you want to make? You can make a mirrorless camera that has every feature of an DSLR, but there is no point to do that if you lose the advantages of a mirrorless system (small and light).