Was Mrs ever intended to mean Mr's, as in mister's to indicate possession? I started thinking about this when someone brought a breakdown of the word history (his-story) to my attention. It obviously would be very sexist but not surprising.
Mrs is the written form of missus. The EtymOnline entry writes that missus is a:
corruption of mistress; as oral form of Mrs., from 1790; the missus “the wife” attested by 1833.
Tracing back further to the entry for mistress uncovers:
early 14c., "female teacher, governess," from O.Fr. maistresse, fem. of maistre "master" (see master). Sense of "a woman who employs others or has authority over servants" is from early 15c. Sense of "kept woman of a married man" is from early 15c.
Where did mister come from? It's a corruption of master :
O.E. mægester "one having control or authority," from L. magister "chief, head, director, teacher" (cf. O.Fr. maistre, Fr. maître, It. maestro, Ger. Meister), influenced in M.E. by O.Fr. maistre, from L. magister, contrastive adj. from magis (adv.) "more," itself a comp. of magnus "great."
So mister and missus derive from the male and female forms of maistre--they share a root. Mrs is not derived from a possessive form of Mr.