Yes, but then why bother? Why bother having any high level diseases since just from the 1/2 per level bonus, not to mention any Aid Other, gets the roll well out of the danger zone.
The fact is that diseases, including high level diseases, _are_ in D&D. It's just that the mechanics then make them pointless, little more than an annoying little speedbump since 150 gp when you're 15th level or higher is chump change.
Let's just say that you're 14th level, and trying to cure a 14th level disease.
You've got a +7 for your level bonus, say, a 16 for your Wis assuming you're not even a Wis based class, so that's a +3. So before you even roll you're guaranteed a +10...and you're not even trained in Heal.
Then you have four of your friends join in...well at 14th level you still only need a 10 for the +2 bonus, so even if you've got no Wis bonus at all, and not trained in Heal either, you only need a 3 to get that 10.
So odds are you're getting either +6 or +8 bonus on top...so you're into the 17-19 range on the skill check, even if you roll a 1. Then you subtract the 14 for the disease level for a 3-5...
So basically at 14th level, in order to have a smidgen of a possibility of dying, you need to have the Ritual Caster not be trained in Heal, have no Wisdom bonus, have 4 friends who try to aid, also without being trained in Heal, have no Wisdom bonus...with all of them rolling a 1 or 2, then having the Ritual Caster rolling a 1 himself.
All the other 'costs' are effectively dealt with via healing surges and once you're low on those just take an Extended Rest.
It gets even worse as you go up in level.