ok, issue solved (I don't know how).
however, giving the pieces of barny to a newly built unit allowed it to cast the "barny resurrection spell".. so I've got back my barny.
and I have now a Barny with 350+xp, vampire promotion (+25%str, allowed to feast ???? yeah), phoenix blood that didn't do anything, and a few other perks

(wonder spell did wonders to my barny)
micromanagement tip for mages and upgrading new mana node
resident mage with mobility & body I (and creation I, creation II, mind I, spirit II, earth I) : 5 turns to boost the city, then 1 turn to get to the node, "build node", cast haste, back to city (the boosting spells are maintained) : rince & repeat : your mage can upgrade the node without losing the bonus to the city enabled by the boosting spells. (alternatively : get your adept to upgrade the node twice as fast : work on node, cast hast, re-work on node)
same (keep your city boost) with uprading desert/ice : have workers build roads, get on roaded ice, burn the ice into tundra, get back to city.
same with working faster : mage+ workers : get workers to work, cast haste, get the worker to work again (they get to work 2 times in the same turn)