Dont be too panic stricken!
There is a fuse in the power adaptor, if the schematic I have is right.. But that probably wont have saved anything much, although, with luck, it might have blown and protected the transformer.
The maximum allowed input voltage for the regulators is about 35V - I believe about 18V is the normal maximum input (but I may be wrong) but anyway, from 240V you will have given the regulators more than they could cope with.
You will also probably have put more voltage across the supply electrolytics (C19 and C20) than they can cope with..
A lot will then come down to luck.. Replacing C19, C20, and the 2 regulators (U1 and U2) may be all thats needed.. This will be true IF the regulators failed open-circuit, and if this is the case, its quite a simple and cheap repair.
If one regulator failed open circuit, one short circuit, you will probably be ok with just replacing the regulators and capacitors as described above.
If both failed short-circuit, then damage could be more extensive - the LM13700 (U3) has maximum voltage rating of 35V (or 44V for A rated parts) so if the supply exceeded this, it could die -
I think you would need to be quite unlucky for damage to go beyond the above - but with this sort of thing it is impossible to absolutely predict what may fail -
I would start by replacing C19 and C20, and replacing U1 with a LM7812 (not a LM78L12) and U2 with a LM7912 (not a LM79L12) .. These beefier regulators will allow one to test for any other failures. If it doesnt work, I would then replace U3.