Try as Jacadcaps suggested and use a ping command from MorphOS to ping the Windows gateway every five to fifteen seconds. Obviously it's not a workable solution, but if your connection stays open then the Windows gateway is at fault.

As for bridging, as I don't know exactly how your network is laid out then my suggestions are limited. I've found bridging to be far more reliable (and faster) than ICS, but you would have to dedicate a whole interface to it. I for example (before my old ISP allowed routers) connected my Pegasos to one LAN card on my PC and a second LAN card on the same PC to a cable modem. The Peg connected straight across as if it was directly connected to the modem. Getting a hardware router was just so much easier.