Saving throw vs death

[Kalgain]

I am theorycrafting a few builds with defense against epic spells in mind. I hope somebody can help me out.

since saving throws stack up to a cap of +20, is saving throw against death/something else stacking with the +20?

since epic spells pierce immunities, it's impossible to defend with protection against alignment (for immunity to mind affecting spells) and death ward (immunity against death effects)

There are some instant kill spells like
https://wiki.bgtscc.net/index.php?title=Damnation
https://wiki.bgtscc.net/index.php?title=Entropic_Husk
https://wiki.bgtscc.net/index.php?title=Mass_Fowl (which kills on bgtscc)
https://wiki.bgtscc.net/index.php?title=Vampiric_Feast

Is it possible to defend against them with +saving throw vs death? (or any other specific saving throw bonus)

If not, what ways are there to build a defense against epic instant kill spells(besides the obvious spell mantles)?

[Blackman D]

ML gets a +10 vs death spells before getting immunity to death spells

then protection vs spells is another +8 via the spell of the same name or shades self