It could happen with this generation vehicle, but it seems somewhat questionable. There are currently plans in motion for Buick to get either a rear-drive sedan based on the Commodore/SS, or to get one based on the larger variant of the Alpha chassis that'll be under the third-generation Cadillac CTS.
Given how close GM is making Buick and Opel, it doesn't seem like a large stretch of the imagination to make that transition quite easy. But, I'd find it somewhat difficult to support that in terms of business sense. As far as I know, there have been no plans to install oil burners to either platform, and beyond that, body variants popular in Europe (estates and hatchbacks) don't seem likely to join the lineup. Unless they are selling them strictly as niche vehicles (as they did with the VXR8, etc), that'd be about the only way they'd do it.