That sounds unusual as in it should only happen if one of the parties actually disappears, ie loses network.
3.0 does not provide sessions, it instead offers the concept of a channel. Both parties can continue to send on the channel indefinitely, regardless of the other side's connection status. When a given user reconnects, he or she will receive any undelivered messages that were put on the channel.
Sessions/presence notifications can still be implemented over this architecture, of course, and we could bring them back if the demand is there.
Links to the betas are on our API site: http://bu.mp/api
Thomas