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.
sorry but im not sure that would work, I dont think the new actress would ever be accpeted, if the TARDIS was to regenerate her, it would have to be into ES again, dont think a 2nd actress could play the role.
The best bet for the show to continue would seem to be Jo Grant.
That said the TARDIS could merge their two minds, so that that Sarah Jane will be part of Jo Grant.
I am sure the TARDIS can take us on a tour of Sarah Janes life, very well however.