I see you've had your first Greydwarf event. Congratulations/Condolences!

Yes, those particular boars are gone forever (the ones that died - the ones that just escaped may eventually be found, usually from wherever you originally got them, if they don't get killed by monsters first). Fortunately, wild boars spawn quite frequently, so it's just a matter of finding and taming a new set. Or, if you still have 2 or more tame boars, beef up the protections around their pen (stakewalls are your second best friend at this stage of the game - ditches and walls made of raised earth being your first) and breed their numbers up.