You can definitely die to a single doll popping. Multiple players in a game increase a doll's health, if they are special mobs they will also have increased health. There's also amp damage curses and crit too.
Meditation on a merc doesn't work when you are teleporting, and it'll pop a doll, so there isn't a reason to use it when running Meph.
You can use a low damage insight but I'd still be scared of it popping a doll.
Here's a video of me with a lvl84 sorc in hell almost dying to dolls. I didn't have a weapon on my merc at all, but if he had killed a single doll I would've died immediately. That's with a 15% DR string of ears and max block build too, by the way.
https://www.youtube.com/watch?v=eaIoKgrUiE8&feature=youtu.beQuote
. Second if you get mana burned you need to have a very low cost on teleport otherwise you will eventually die, because you will get mana burned and then stuck. With low teleport cost and meditation you can just teleport away even if your mana reaches zero.
If you get mana burned a low mana cost teleport won't help either. Chug mana pots and if you get burned you can always just leave.
I get what you're saying about putting points in teleport, but that juice just ain't worth the squeeze. 20 skill points can be put into much better places.