Amusingly the PHP manual contains an example that tries to recreate the original structure from the print_r output:
print_r_reverse()
http://www.php.net/manual/en/function.print-r.php#93529
However it does depend on whitespace being preserved. So you would need the actual HTML content, not the rendered text to pipe it back in.
Also it doesn't look like it could understand anything but arrays, and does not descend. That would be incredibly difficult as there is no real termination marker for strings, which can both contain newlines and ) or even [0] and => which could be mistaken for print_r delimiters. Correctly reparsing the print_r structure would be near impossible even with a recursive regex (and an actual parser) - it could only be accomplished by guesswork splitting like in the code linked above.. (There are two more versions there, maybe you have to try them through to find a match for your specific case.)
