Against the odds -- at least if you go by the consensus among lawyers in Brussels before this case was heard
The Advocate General opinion is followed in the overwhelming majority of case.
BUT the exceptions tend to be the ones that are, well, more politically charged
There are many legal risks taken in the draft withdrawal treaty.
There will be many more in future EU/UK agreements
And in the end the ECJ can step in, and toss it all out, just as it did with the first EEA deal in 1991
eur-lex.europa.eu/legal-content/…
Not even the ECJ is "independent" enough from political reality to release an AG opinion with big implications for UK debate in full expectation that it will be completely ignored.