We should replace the check of WT_TS_NONE with the helper function as the previous check is not very easy to understand:
if (vpack->tw.durable_start_ts > rollback_timestamp ||
(vpack->tw.durable_stop_ts == WT_TS_NONE && prepared))
else if (vpack->tw.durable_stop_ts != WT_TS_NONE && (vpack->tw.durable_stop_ts > rollback_timestamp || prepared))