i think it would take a party of eight to get the full health possible
W/N - endure + defy pain, that necro skill to get more hp i forget what its called
R/Mo - maxed out symbyosis
R/Mo - maxed out fertile season
Mo/X - enchants (max 7 and blessed sig) x3
(not sure if there are 21 monk enchantments, im almost sure there arent 21 sustainable enchantments, but i'm pretty sure that enchantments such as healing breeze trigger symbyosis. i think that there is a 10 enchantment maximum to stop stuff like this [i think it was mainly to stop ether renewal stuff though] but i dont know if that applies to stuff such as healing breeze, guardian, etc. it would take good timing to get all of the enchantments off at the right time and such, but hey

N/Mo - necro enchantments (dark aura, i think there are more), maybe leftover monk enchants
E/Mo - windborne speed (pretty sure its an enchantment) and also any leftover monk enchants
so, supposing the warrior had 455 hp (superior vigor and a superior strength rune) i think the health would be as follows - (assuming that only ten enchantments can be maintained and symbyosis is at 125[max i think])
base health - 455
hp mod on weapon - 30
hp mod on sheild - 45 (while enchanted of course)
fertile season - 210 (i think)
endure pain - 300 (i think)
defy pain - 300 (i think)
vital blessing - 290 (from the monk with max prot)
demonic flesh - 176
10 enchantments and symbyosis - 1250
= 3056 (pardon me if my math is incorrect)
now, supposing that we can have 7 enchantments from each of the three monks, all timed correctly, and three from the necro, and that windborne speed is an enchantment (and that more than 10 enchantments on one target is allowed) the total would be something like this
25 enchantments from symbyosis - 4125
3056 - 1250 (ten enchants and symbyosis) = 1806
1806 + 4125 = 5931 health
please post if you know the enchantment number or anything, and correct any mistakes i've made =) id like to play around with this later