"solo" instance running and open PvE, etc.?
The Question still is..

how do you want to do an instance run without a tank and a healer?

you only want to run through instances where the mobs are grey so you can handle them without getting too much damage (like running through the deadmines when you're level 40)?

you can't handle a heroic elite mob / boss in a heroic instance without a solid tank and a healer class because he will one-hit you or your warlock-demon.


so which PVE Content do you want to handle?
Just questing?