Helldritch
Hero
1) Having the whole keep on you is not what you want. You will get 12 to 16 (sometimes more) equivalent of encounters. You will die.um... okay but most my parties are only useing suprise on a case by case (both as player and DM) so that isn't much of a con to my groups
perfect that is what we want... that is a pro we are drawing them out and spliting them up.
okay and they will be at full fighting shape and you will loose your 5th level caster...
okay so game over, and we start again a new campiang... no big loss
I have never shown my notes before... unless it was to help a new DM in training... but even then I can't imagine why the Players would care as they are already makeing up there new characters... and in my experence these new characters will just be more OP and more tactics oriented that will lead to more 5mwd.
again I can't imagine this tactic working... and if you TPK enough players will just find other DMs
2) You will not be at full strength as you still have not finish your long rest. That caster might even be already more than 60 feet away as he would dispel then move away. That caster will out of the range of most darkvision range.
3) I would show my notes and indeed I did on more than one occasion, with a new group that tried the 5mwd and got TPK and was outraged to have been killed so. That was before the 5 mwd was defined and a thing. When players see how not doing the 5 mwd would have saved them lots of trouble, they start to realize that this playstyle is not welcomed unless the story calls for it.
And most players like it when the DMs share their notes. It shows that what they faced was written and not added on the spot to "justify" a TPK.
4) With dark and gritty games, TPK can and is a thing that can happen. Character's are frequent at low and mid level and start to disappear around 9th to 12th level.
5) A lot of your solutions involves high level magic which might not be the case. Teleportation, unless circle is quite high level and even the circle takes time to cast and requires components. You play with components don't you? Components that might run out quite fast if tactics you decscribe are used on a regular basis. My second group is reaching twelfth level and both wizard can cast teleport circle four times before they run out of components.
6) As for players leaving my games. This happens very rarely and usually because that player is moving to an other town. Some of my players were doing 1h30 of driving to come to my games. I had to have a room ready for them as they needed a place to sleep. Now they are in an other town at the other side of the country. So the death toll is not a deterent for many players. The challenges and the fairness with which I DM is the feature that players playing with me are looking for.