No, BioWare hasn’t made an official announcement on a potential Mass Effect 4 and officially,
Mass Effect 3 hasn’t even launched yet. Those facts aside, judging from previous experience, it is probably a good idea to consider keeping a hold of your save files for Mass Effect 3 once you finish the game. Even BioWare’s own Mike Gamble thinks that it might not be a bad idea.
In a recent interview with
Gamerzines, when asked about whether gamers might need their ME3 saves in the future, Gamble was quoted as saying, “Obviously I can't say anything, but it wouldn't be a bad idea ...”
It has already been stated that Mass Effect 3 is the end of the Commander Shepard trilogy, but that doesn’t mean that the Mass Effect universe in itself won’t live on. We never know what is coming down the road, especially with a serious as successful as this one, so do yourself a favor and stash you save file somewhere safe when you finish the game.