The fact that the MP aspect of ET was released for free is the best advertising I can think of for SD. Talk about endearing yourself to gaming community. It shows the talent of SD as a whole and because they were able to do their part and make a solid MP even though the project as a whole failed. Now they are working on the next generation Doom3 type stuff way ahead of the pack so IMO, it was a smart decision.
Also, I wouldn’t say ET is totally unsupported. There are these forums, tons of fan and clan sites, a custom map editior, and so on.
I think the gaming community as a whole will be seeing a lot more of SD in the years to come.