I have to say that I don't remember the last time that this happened.
Gatwick-Guernsey - BA pulled off, Aurigny took over slots/route, BA hasn't returned.
Gatwick-Rotterdam - BA pulled off, TTG took over the slots/route, BA hasn't returned.
Gatwick-Plymouth - BA pulled off, Air Southwest took over slots/route, BA hasn't returned.
Gatwick-Cork - BA pulled off, easyJet/Ryanair later both came onto the route and slugged it out, Ryanair won, easyJet withdrew, BA hasn't returned.
Gatwick-Shannon - BA pulled off, easyJet/Ryanair then slugged it out, Ryanair won, easyJet withdrew, BA hasn't returned.
Gatwick-Newcastle - BA pulling off, Jet2 taking over using slots etc redeployed from MAN/LGW.
Heathrow-Belfast - BA pulled off, bmi increased service then moved to BHD. BA hasn't returned.
Heathrow-Jersey - BA pulled off + increased LGW/JER, bmi starts LHR/JER 26Mar, BA hasn't returned to LHR/JER.
Heathrow-Inverness - BA moved service to LGW, bmi started LHR/INV, BA has maintained service at LGW and to be shifted to Flybe as part of BA Connect transfer. No BA outrageous actions there.
Heathrow-Bremen - BA pulled off, CityFlyer picked up route from LGW, BA pulled off that after taking over CityFlyer. Ryanair/easyJet now in war between STN + LTN for Bremen route, BA hasn't returned.
Heathrow-Hannover - CityFlyer started alongside BA; BA pulled off LHR; BA took over CityFlyer and later pulled off LGW-HAJ as well. Air Berlin quite happy operating HAJ-STN and no sign of BA returning.
Gatwick-Dusseldorf - BA pulled off, haven't returned. New carriers have started inc LH on LCY-DUS.
Gatwick-Munich - BA took over route which Deutsche BA started, haven't returned.
Gatwick-Genoa - old BCal/BUA route operated by BA for years, Ryanair came along on STN-GOA and BA pulled off, haven't returned.
Gatwick-Bilbao - moved from LHR, Go/easyJet came along from STN, BA pulled off and haven't returned.
The only routes which I can think of where BA has operated, pulled off, and then returned to the routes at a later date (like Newquay) are Vilnius, Riga, Zurich and Salzburg. It has since pulled off both of the Baltic routes again and this winter is its first on LGW-Salzburg again, where admittedly it is competing with Thomsonfly. It only went back on LGW-ZRH after easyJet had pulled off due to high airport charges at ZRH.
Compare that to routes on which BA faced no competition in the last ten years and had a monopoly either from LGW or from LON in its entirety, and now faces competition:
Naples (bmi + easyJet)
Verona (Ryanair)
Venice (easyJet, Ryanair, bmi)
Bologna (Ryanair/Forli)
Pisa (Ryanair)
Edinburgh (easyJet LGW)
Glasgow (easyJet LGW)
Inverness (bmi LHR, easyJet LTN)
Marseilles (easyJet LGW)
Toulouse (easyJet LGW, Ryanair CCF-STN)
Bordeaux (easyJet LTN)
Geneva (BA monopoly on LGW, easyJet appeared)
Krakow (every man + his dog)
Nice (easyJet LGW)
Athens (easyJet LGW)
I can't immediately think of any others, but I'd be hard pushed to quote any example of what you seem to be suggesting. Bear in mind that Manx/ BRAL / CitiExpress / BA Connect route planning has been autonomous of Waterside for several years. GBALU53, just out of interest, can you actually suggest where this has happened before? Granted, the above doesn't paint a pretty picture of BA's management of regional routes (or lack thereof). It might well be incompetent, but I can't see that it's predatory.