Welp, that is super unfortunate.
Hope your wrong about 'never' mikeledo.
I think he mostly meant that you should operate on the assumption that you will not be able to get those evolution artifacts rather than on the assumption that you
would be able to. It prevents you being very disappointed later on if they are not available.
There is really no way for any of us to know if those evolution artifacts will become available next spring again or not. My personal advice would be to keep the base buildings and evolution artifacts in your inventory. If you already placed the Fire Phoenix, you could sell it and then craft it again in the MA to keep in your inventory. Or keep it out at a low level. It is still useful.
Others can correct me if I'm wrong, but the bears were the fall event, yes? If they also repeat that event style, then there may be bear evolutions coming in a few months.