In pseudo-Apollodorus' version, Medusa's sisters sought revenge on Perseus, who escaped them by using the Cap of Hades (which rendered its wearer invisible):
So Perseus put the head of Medusa in the wallet (kibisis) and went back again; but the Gorgons started up from their slumber and pursued Perseus: but they could not see him on account of the cap, for he was hidden by it.
Source: Apollod. 2.4.3
Also, at least according to Hesiod, Medusa's sister were immortal:
And again, Ceto bore to Phorcys the fair-cheeked Graiae, sisters grey from their birth: and both deathless gods and men who walk on earth call them Graiae, Pemphredo well-clad, and saffron-robed Enyo, and the Gorgons who dwell beyond glorious Ocean in the frontier land towards Night where are the clear-voiced Hesperides, Sthenno, and Euryale, and Medusa who suffered a woeful fate: she was mortal, but the two were undying and grew not old.
Source: Hes. Th. 275