What the Fuck!, should have gotten 2 x 2 slice toasters so if that situation crops up, you plug the second one and all's well, plus if one should fail, then you are not left high and dry, well in this instance. You should have used the CRO rule, always get at least 2 CRO's , the 2nd one to help repair the 1st if it fails
Seriously though, that really is a bad design flaw, it should have been treated as basically 2 x 2 slice toasters but sharing a case. The not only would it be "green" because you would only be using half the elements if you only wanted 1 or 2 slices, but if the scenario you describe happened, then you could drop extra slices in and they would be ready independently of yours, thats a serious design fail right there.
On other news, more TEA related, today I got my RS invoice for the calibration of the 3478A, the cost was £0.00 and seeing as I was able to do a self calibration using the limited equipment I have to hand, and it seems to be reasonable as it concurs with the various references I have and also of course the plethora of other meters, I'm kinda thinking that this needs to be flagged up to someone at RS in authority in order to prevent this from happening with anyone else's meter and it might also throw into question the validity of some of the meters that they have done and issued certificates for?