Isn’t the whole point that when the client roams it opens a brand new L3 connection to the server, then sends over L4 packets to reconnect the L4 session over the new L3 link. Thus keeping L4 session state separate from L3 routing mechanics.

As for L3 packets going into the void. Yeah they’re gonna get lost, can’t be helped. But the server also isn’t going to get any L4 acks for those packets. So when a new L3 connection is created, and the L4 session recovered, the lost packet just get replayed over the new L3 connection.