When the Khmelnytsky Uprising began in 1648, Łaszcz fought against the rebels as part of the Zasławski party. However, his enemy, Prince Wiśniowiecki, demanded that he leave the army camp, due to an event that took place before the Battle of Pyliavtsi. Łaszcz, having 1000 men at his command, had attacked the Cossacks' camp, causing alarm and fear. He left but later fought in the defence of Lwów, scoring some successes against the besieging Cossack army. The Polish lower parliamentary house (sejm) granted him a "salvus conductus" (safe conduct) in return for his military services; however, he only participated in the campaigns of 1648, before falling ill and dying on 15 February 1649. He was buried at the Saint Stephen Church in Kraków. The church was demolished in 1802; thus, Łaszcz's tomb has been lost.