Disappearing Ink should be defined as:
Any ink that is no longer visible afer reasonable handling or use
We are not saying that receipt providers are using trick ink or engaging in deception, just that it is not fit for purpose by the standard expectation for the lifecycle of a proof of transaction.
In the United Kingdom businesses are required to keep a receipt of transactions going back 6 years for tax purposes. When I noticed my receipts fading from thermal paper a slight panic ensued - especially as some of the amounts were significant (ie over USD$100/GBP£75).
However proof of a transaction does not necessitate a paper receipt. As many transactions are now by card a bank statement would attest to the fact that you had spent that amount and to the receiver of the funds.
In Italy if you are not given a receipt by a retailer or restaurant you as the purchaser can be fined (along with the offending restaurant/retailer) if the transaction is found to be off the books.
The Guardia di Finanza are rumoured to wait outside of restaurants suspected of 'cooking' the books to catch unlucky patrons and compile evidence against the offending company.
Long story short:
No there are no laws I am aware of that discuss the visibility of receipts over time.
Yes in most jurisdictions sellers are required to provide a legible receipt of transaction at the time of sale, detailing who they are, any tax applied, and their tax reference.
I imagine you could consider litigating for damages if the receipt was a vital piece of evidence for you in a case where you are attempting to prove that you had not committed fraud, and that it became unreadable through the negligence of the receipt provider in under a year. However the likelihood that this one receipt would be the salient piece of evidence is less likely that me scoring a touchdown in the next super bowl.
Or just try heating up your receipt with an iron/hairdryer ( I accept no liability for this, it is a joke suggestion)