Given that during the recording of the next album (
Saints & Sinners) following that tour, DC basically disbanded the then Whitesnake line-up for a period of self-contemplation and strife with the management, only to then rehire just parts of the band going forward (Jon Lord and Micky Moody, but not Ian Paice, Neil Murray and Bernie Marsden), I'm not so sure whether Jon and Ian might not have regretted negotiating good contracts with Billy! Because even Jon Lord must have had second thoughts when he found out later that Cozy Powell was on a higher wage than him with the new Whitesnake line-up. You don't do that to ex-DP rock royalty!
Ian Paice didn't want to reconquer the US from the ground up - he had done that with DP already, endless tours of DP opening for The Faces etc. DC was still hungry though (and would eventually achieve his goal of course). Billy Squier's busy US touring schedule might have been an issue, but in the early 80ies he was easily the more established and hopeful act who could offer higher grade gigs for British rock royalty. Musically, I could have seen it work, but of course Billy's band mates were no slouches either. The late Bobby Chouinard as Billy's then drummer especially had quite a reputation. But both Ian and Jon were adaptable musicians, they could have slotted right in. (Jon wasn't always happy with his role in WS, the constant twin-guitar-attack gave him a lot less freedom than with Ritchie in Purple, the latter leaving a lot of space for Jon due to his sparse rhythm guitar playing.) But of course, Coverdale was a fellow-Brit and a former band mate turned band leader - that provided for some glue within WS.
When after the DP reunion in 1985/86 a journalist at a WS press conference innocently asked whether Coverdale had "
contributed anything" to the Mk II reunion (at that point he hated any mention of his DP past), a suitably irritated DC snapped: "
Yes, JON LORD !!!"