No, though no case u/s 498A IPC could be filed unless thecomplainant is married to the principal accused , once the case is started and during pendency of it divorce is obtained the same does not make the case u/s 498A IPC cease to exist.

A marriage can be solemnised either by making rites and rituals or by Registering it under any Marriage Act. Once a marriage is Registered under Act, it becomes operative and no matter whether the couple stays a single day or not without taking divorce any subsequent marriage by either of the two is illegal.

No. An agreement can validly be executed either by entering the offer and acceptance in writing or verbally. If two persons agreees on a certain thing on verbal terms then the agreement is very much valid and operative.