Well, my opinion is that the LP should not be a unionist party. It should have supported self-determination in Scotland. The nationalist vote up there rests a lot on socialiists who have found refuge from Blairism in the SNP with it's mildly collectivist approach to politics. Scotland could be a sovereign nation who are leftist by proclivity. Just let them go.
That wont happen though because the LP nationally (Uk-wide) need Scotland to get control of Westminster. As said, the SNP could be in for a spell of blood-letting now and that can help Corbyn into No10.
I agree with most of that mate. However politics is about more than crude numbers. If Scotland went there own way, built a broadly left, inclusive country then it would show clearly to lots of people in England that it was possible. I think it would snap some sections of the left out of desperation.
The other thing is that the Tories won 2015 in no small part down to the fact of attacking Scotland and it's links to Labour. Take them out of the picture and there is that option removed.
Labour need to start connecting to people in England. It won elections in 1997, 2001 and 2005 in England and would have had a majority without Scottish Mp's. It can be done. The Labour party post 2010 has already been increasing it's vote in Ruk and that trend dramatically increased in 2017.
I think the pessimism if "we can never win without Scotland" is not only untrue, but deeply unhelpful and has to be challenged.