Offline talker you mean or what?
If you mean offline talker -- the answer is: no. It is "illegal" feature, and patchou won't do that.
If you mean like: send a message TO offline contact, and he/she will get it when he/she signes in -- thats a good idea. It is possible while your PC is on, and you're signed in; so messages can be stored in physical memory or hard drive, and send later. But its not possible if your PC is off. Why? -- message needs to be stored somewhere, on a server, that does not exist (at least not at the moment).
But if we talk only about the time when PC is on and and you are signed in, suggestion is really very cool