Improved familiar + banishment / dismissal spell

[blahpers]

Suppose a wizard 7 has an imp/quasit/archon/whatever familiar. An enemy cleric casts dismissal on it. The familiar fails its saving throw.

Is that pretty much it? Time for a new familiar, or a scroll of plane shift/lesser planar binding/whatever to get it back?

Bonus points if it's a witch instead of a wizard--they just lost their spellbook. o_O

[DeathlessOne]

That is a clever cleric. Technically, unless you dismiss your familiar you can not get a new one, even if it is on another plane. Just avoid the problem and keep your familiar out of combat so it isnt targeted.

[Myrryr]

Well, for an outsider improved familiar, part of the binding ritual does include calling them from the outer (or inner, in the case of an elemental) plane.
I don't see a reason why a wizard couldn't go through the first part of the ritual to call the imp or whatever and just stop there. It should work fine.

Alternatively, since a familiar is utterly incapable of disobeying a direct order, you can just get your familiar's Truename, and if you have an outsiders Truename, you can call them to your side by speaking it whenever you want, according to the Wizard Arcane Discovery.