When can you feel sure that they're gone forever?

Hello to you all! I haven't posted here for a long time, hope everybody is staying strong and making progress in their recovery.

I got out of the abusive "relationship" with the N/P last year, I just got fed up of the games and was quite drained and couldn't really take much more of it. It was strange how it ended though, I was still attending her fitness classes but once I realised that it was just a further opportunity to play games and devalue me further I stopped turning up, then I ignored her group texts that she continued to send for about a month.

The last visual encounter was just before Christmas when she looked startled at seeing me and practically ran away. I was convinced that was the last of her but I received an "accidental" text back in January, on the day after my birthday no less, so then I blocked her.

It's been almost 6 months now and since then I've been in therapy, trying to take care of myself and getting stronger. I still have the distressing dreams but overall I'm doing much better. However the other day I was alarmed to spot the ex N while I was out shopping, before she had a chance to see me I hid in a bus-shelter (I know! I obviously haven't reached the stage of indifference yet) because I was afraid, anyway since then something has just felt "off" and I feel a little on edge and have been having strange dreams, I haven't heard anything for six months and I feel strongly that she has new supply, so is it safe to assume that this recent near miss means nothing, was just coincidence and that she's gone for good? I don't think she returns to past sources after finding a new one.