Normal adult bladder volume ranges between 300-600mls. Some medical sources suggest up to 500mls.
4 hikers were found dead in a watercourse, and two of those were found to have 600mls (Semyon) and 700mls (Alexander) at autopsy. Nearest the ravine was Igor, who was fit-to-burst with a litre.
It's perfectly possible that Lyuda's bladder may also have been full, but the pathologist omitted to record hers at autopsy, and Tibo's was the only one found to be empty, likely the result of his serious head injury rendering him so deeply unconscious that he lost control of his bodily functions and urinated on the floor of the ravine, but for all we know he too may originally have had a full bladder.
Of the remaining 4 hikers all were within normal ranges, although Yuri K was on the high side at 500mls, and it may be that Rustem urinated after collapse, his right arm outstretched untypical of a conscious man dying solely of hypothermia where he'd tend to adopt a semi-fetal position to reduce his bodyprint offered up to the cold, and this may have helped generate an ice pad underneath him.
It seems strange that up to half of the hikers had full or overloaded bladders other than the logic that they drank copiously from the ravine, and I wonder how this autopsy observation fits in with theories about wolverines, tree collapse, KGB or other third party attack.