The way money is re-shored is whenever a US President (so far only republican Presidents) decide to give companies a tax holiday. So far Bush and Trump gave such holidays. Which means that corporate treasuries only have to wait for the next Republican president to re-patriate their off-shore cash. During this time corporations usually use debt to service dividend payments, share repurchases, and operating expenses in the US.

https://en.wikipedia.org/wiki/Repatriation_tax_holiday