Comment 1 for bug 685885

You have mingled two issues in one report.

(1) Enblend does not warn early, if the output image
will overwhelm the selected output format.

(2) Neither Enblend nor Enfuse clean up a half-done
output image, if they unexpectedly die or they are
interrupted by the user.

Issue (1): In the general case this is a complicated
problem that requires (a) finding out about the
final image size as early in the process as possible
and (b) knowing the size limits of all possible output
image formats with respect to their actual libraries.

Issue (2) should be fixed in rev236fd8c3e767.