While no one can replace Elizabeth, I'd really like SJA to continue somehow. I know it's a kids show, but I really enjoy it, and like those kids in those roles, and hate to see it end. I also would prefer to think that Sarah Jane herself lives on in the Whoverse, even though Elisabeth is no longer with us.
So perhaps upon learning of Sarah Jane's passing, the Doctor's heart(s) break. And so too does the Heart of the TARDIS. After all, Sarah Jane was its companion too. And for a longer time than most.
From what I know of the Heart of the TARDIS, it is alive in a sense, and telepathic, and can essentially grant people's innermost wishes for them. And no one, not even The Doctor, knows for certain how it works, or how far its power extends.
And perhaps the breaking of hearts leads could lead to the breaking of rules. And... I know its just a stupid fanboy fantasy borne of my sorrow for Elizabeth Sladen's untimely passing, but maybe, just maybe, the Heart of the TARDIS could intervene and grant an old friend the gift of regeneration.