Mr. Adventure wrote:
And the Doctor can never see again. Between her and Rose I get the feeling that RTD doesn't like people playing with his toys.
From reading The Writer's Tale
, I suspect that had RTD known Catherine would be willing to return in the future her fate would've been different - that it was a way to explain why she wasn't returning in future return-of-all-the-Companion episodes, rather than breaking his toys on the way out.
If true that seems both short-sighted and somewhat misguided (rigid adherence to logic seems not to be a top priority in Who). Even so, a noble(ahem) sacrifice would've been more worthy of the character progression and growth than to have all her fabulous experience stripped.