Assuming both halves have the same serial number printed on them, yes - a glued back together torn bill would be valid. You may exchange it at any US bank. If banks don't want to deal with that - send it to the BEP. If you only have one half, and it is exactly one half - then it is useless. That is why the person in the comics said that his halves are useless to him. The banks or the BEP will want at least most of the paper currency to replace it.

The act itself (tearing the physical currency intentionally) is a felony with up to 5 years in the Federal prison.

Assuming both halves have the same serial number printed on them, yes - a glued back together torn bill would be valid. You may exchange it at any US bank. If banks don't want to deal with that - send it to the Bureau of Engraving and Printing (BEP). If you only have one half, and it is exactly one half - then it is useless. That is why the person in the comics said that his halves are useless to him. The banks or the BEP will want at least most of the paper currency to replace it.

The act itself (tearing the physical currency intentionally) is a felony with up to 5 years in the Federal prison.