This has happened to me twice. Both times were completely out of my T's control but ended up with me having several weeks out of therapy. I didn't so much feel abandoned because I knew nothing that happened was within T's control (I could rationalise that well by then), but I did feel massively upset, both due to not seeing her and what was going on for her to have to cancel the therapy. T kept in touch throughout which helped a lot even though I had no idea when therapy would resume. It did after some weeks in both cases and it didn't affect our relationship at all apart from leave me with more excessive anxiety for a long time.

I don't see feelings as being right or wrong, fair or unfair, they just ARE and they act as messengers for what is going on for you. If you feel abandoned that's probably natural based on past experiences or expectations. It's okay to feel whatever you feel and a good T will know that too.

As far as duty of care goes, that is a hard one. I do feel that my T could have been more forthcoming here, but then considering what was going on for her, I can totally see why she wasn't. A T should, in theory, explain that they are going to have to take time off and advise you to seek additional or alternative support in the meantime or even recommend a back up T. They should give you a point of contact if they are unable to be in contact with you themselves. They shouldn't just leave you without anything because a therapist needs to avoid additional harm to a client where at all possible. Life happens, a therapist needs to take time out sometimes, but they should at least take steps to keep the client informed and advise on seeking other help if needed.