But both of those both lead to the same scenario: the wizard in his tower, on his plane, who sends out Astral Projections to handle any outside interaction. He can unleash hordes of undead, gated solars, simulacrums, other constructs, Ice Assassins (even if we don't allow it to convey deification). The wizard 'in the party' doesn't have to be 'within physical proximity to the party.'
I can't think of any reason why a wizard 'in my party' would ever be outside his tower. At this level of play, long, drawn-out excursions (actually, excursions of any kind) are beyond necessary and are quite foolish to anyone with a 30+ Intelligence. They're not going to be on a romp through the woods, or sitting in the pub. Even in a party type situation, these are some of the wealthiest and most famous people in existence. They're forced into seclusion one way or the other. Either through adventurers wishing to relieve them of their wealth, or evil forces (or good forces, as the case may well be) wishing to purge the world of the threat to their own power.
These people really only need to 'do things' when the world is in danger. Even if they are a party.
That does not require the wizard to leave the safety of his home.