Is it possible to have an alliance which does not buy tokens, but still manages to capture all relics? Has this ever happened?

i dont think it has happened but it could but unlikely

Every top alliance has a donater or a few. But I know of a few people that have finished in the top 5, and never donated. Off the top of my head I know JasonFri13thx, and MilinorX. There could be more, but I've only been playing BD for about 3 months

It is possible actually. Most top alliances have supporters, but it has happened. Apollo finished 5th with a relic before.

zal ranked 2 without donations i think

How could I forget Zul? He finished 3rd without supporting, he had a relic.

USMC E6 old client

I finished 2nd with 3 relics and never donated in my 2+ years od BD

~Riders of The Storm

It is of course possible most top alliances win by a lot so if they had no supporters then they could easily still win with less power over the 2nd alliance.... but it does not happen often.

last round on e3 i was in SoLD we had supporters one being are number 1 member but they barely supported as far as i know and we won big time so without them and there supporting we could still have won so i dare you to go and get a alliance together and name it NS no supporters and see what happens that world will probably have most supporters being as the other people will support non stop to catch up with yall ..

In theory, it IS possible, but it's only been done a handful of times.