Were the Go pilots on any BA master seniority list? If not, has a precedent been set?
No and no. Go was a low cost airline. BA European will be operating mainline aircraft (two mainline 757s have already been earmarked, possibly with 767s to follow) with the mainline BA product. Ergo, they should have mainline pilots.
IMHO, the same should have applied to BA Regional however the Scope agreement previously allowed for sub-100 seat aircraft to be outsourced away from LHR and LGW (BA Connect initially and subsequently CitiExpress). They have some seconded mainline Captains.
BA World Cargo (GSS) seconded mainline commands are limited to 2/3rds of GSS commands and the agreement is that all the BAWC flying will be brought back to mainline if there becomes a requirement for more than four 747-400s.