The output of fclose() is not suppressed, because there is no reason to suppress it. ans contains the uncaught output of the last processed command. Even from a MEX-function the first output can be replied even for nlhs==0 and the output appears in ans. The trailing semicolon suppresses the output to the command window.
Perhaps your problem gets clear, when you explain, what you want to achieve.
BTW, although I do not know a reason why fclose should fail, it is a good programming practice to catch the output in general to check for errors. I use this in larger functions:
fid = fclose(fid);
Then fid is set to 0 or -1 and a further usage is blocked. Example:
fid1 = fopen(File1);
fid2 = fopen(File2);
...
fid1 = fclose(File1);
fwrite(fid1, rand(10)); % Typo! It should be "fid2"! But error is caught.
Well, although this helps to write cleaner code, it is still not clean: The replied flag is a flag, which is only accidently an invalid file-ID. Better:
status = fclose(File1);
if status == -1, error...
A drawback of fid=fclose(fid) is that MLint warns about an unused variable, if fid is not used afterwards.
