The first technique of providing a DC level to the PIC to indicate mains present should suffice in your case. However, I do not see the need for it to interrupt the code.

Secondly, you seem to be coding totally in assembler. So, I think this thread should be in the Off Topic section of the forum.

The technique of declaring the string in a readable fashion makes more programming sense as it is easier to spot while modifying your code later and will be more compact in flash and execution time too.

Good luck