And if they do that... Thre's some VERY juicy targets in the Karelian peninsula to retaliate in kind, such as in Vyborg and Koivisto oil refineries and gas relay-stations and it's not like St.Pete itself is far from Finnish artillery POV.

Though realistically anything like that to happen would mean that diplomatically things would have already gone sideways and been gang-raped in a dark alley with a blunt object between EU/Finland & Russia.