[MENTION=23716]Gadget[/MENTION]:
but the "big boom" spells are not the problem. It's the "problem solving" spells that greatly enhances a party's capacity for transportation, information gathering, obstacle bypassing etc...
By "big boom" I meant the potentially game breaking spells, not mere damage, sorry that was unclear. There are still those spells, depending on how one would categorize them. But keep in mind that in your Vampire case, both
Plane Shift and
Teleport are 7th level spells. You only get one of those a day. And you have to be a, what 13th or 14th level caster to get them. So you are paying a significant opportunity cost to cast them. Of course they could just cast
Demiplane and toss the body of in the newly created place and forget about it. As long as you don't go to that specific Demiplane again, the new Vampire Lord is trapped there. But that is an 8th level spell.
Forcecage the body in a sunlit meadow, use
Wish to extend the spell duration for a long time (DM dependent, and not very resource efficient), problem solved.
Disintegrate the body, even burn the body and mix the ashes with holy water? DM dependent. These issues remain, to a lesser degree than previous editions.
But lets suppose that there was some opposing force that was preventing the party from obtaining the body. Does the caster enter the fray, purposefully holding back his one 7th level slot to use later, even if things are desperate? Obviously, this decision becomes easier if the caster has 8th and 9th level slots, or if there are more than one caster capable of casting 7th + level spells.
I think the question I was trying to get at before was, do they need to use that 7th+ level slot, or can they get by with not using it to win the fight by relying lower level slots + cantrips. Obviously, other party member contributions will be a major factor, but I think the design intent with no auto scaling damage and effects (you have to use a higher level slot to get more effects in addition to things like concentration), it might be feasible to force this kind of hard choice on a caster. I'm not sure they succeeded though, if that indeed was the intent.