Are you not getting the UK Druids confused with the Gaulic Druids which I do understand to have had Tribes that were Allied with Rome until they Revolted under Vercingetorix. After winning the Siege of Allisium in about 52 AD, Julius Caesar then Massacred the rest of the Gaulic Tribes in a similar way as they did with the UK Druidism.
No, not at all. In terms of Britain, Julius Caesar did not actually see or conquer very much and then there was nearly a century of non-Roman presence, basically a token client king relationship with a couple of southeastern tribes until Claudius arrived nearly a hundred years later. However, if Augustus, Tiberius and then Claudius were all issuing punitive measures and laws against druids, we might fairly presume that Julius Caesar hadn’t wiped them out. Not all of the British tribes had a hostile relationship with Rome at all, but then heroic epics and glorious histories are not usually written about quiet tribes who didn’t get involved in conflicts, certainly not by ancient writers anyway.