But that's in spring. Wouldn't the coming warming, albeit a short warm season, allow predation and deterioration?
Not if the carcase sinks into the permafrost. Gets covered with muskeg (no oxygen) and gets frozen even in mid summer.
Siberia is generally fairly flat, and in such places holes tend to get iced over, (often year round) OR muskeg forms a layer over a small lake or hole. The muskeg might be 10 feet thick but its floating. Big animals call fall through (or little animals in the case of my little brother who had to be pulled out of a muskeg hole while picking blueberries one year), and sink to the bottom where the lake may never thaw.
Flowers do not necessarily mean spring. There are flowers up here that bloom late (since summer is so short).