If things continue as they are, it is very difficult (as ichkeria mentioned) to imagine Labour recovering their position in Scotland. Save any major disasters, I think we're safe in assuming that's going to be SNP land for at least a couple more election cycles.
What is not inconceivable, though, is the prospect of Corbyn forming an alliance with the SNP. Ed Miliband was offered this multiple times during the last election and refused - had he accepted, he would probably be Prime Minister now.
Of course, the SNP are in a much stronger position now than they were before 2015, so if they make a similar offer to last time it will be with more strings attached, and whether it goes through would depend on the Labour team who are negotiating it.
On the one hand, SNP make it much easier for Labour to win office - but will probably ask for another Indyref in return (assuming it hasn't already happened). On the other hand, SNP have also reached their peak strength. They cannot win any more seats than they already have, and it's only a matter of time before their position weakens.
So all things considered I'd say a Labour win in the next election is very possible - but not on the party's strength alone. I also think the likelihood sharply diminishes in the event that the govt waits until 2020 to have the election, rather than calling one in the nearer future.