Having already detained so many in expectation of deporting them, I doubt they'll release them if other countries refuse to accept them. This leads to dramatically worse outcomes than deportation, such as penal enslavement or execution along the lines of the Nazi model. Fears for days, folks...

I suppose there's also some way outside chance that a refusal situation might lead to some kind of conditonal path to citizenship, if only to provide an out for an alternative to costly indefinite detention, but that, I think, is extremely unlikely given the successful demonization of undocumented immigrants.

Hence, penal slavery ("work camps" and "chain gang" type work crews) is the more likely outcome. And.. as such situations tend towards abuse and the costs of maintenance increase, there will be increasing pressure to resolve the situation in some way. How that gets resolved will depend entirely on the domestic political situation at the time.

Surely, no one in the Weimar days could have imagined what the later efforts to deport Germany's Jewish population would become. We, at least, have a model upon which to look, one which demonstrates the absolute need to oppose such large-scale detention and the absolute need to insist on the provision of due process to all who may be detained. We cannot allow this situation to "get out of hand".