When I became System Administrator at the now-defunct E-Z Rent-A-Car, there was no WAN. Sites were using locally-setup routers without proper firewalling or rules in place: one site was even using public IPv4 addresses on workstations. It took several steps to mitigate this situation, given a limited budget + need to stabilize things.
Rental counter workstations were steadily migrated from XP-Home to Ubuntu-Linux installations.
During the Summer of 2007, several older computers were set up at remote sites to use as local caching and relaying for on-site units.
Programs were located to route critical IPv4 traffic over the IPv6 WAN, as needed. Concurrently, printers were migrated to IPv6-enabled Brother laser and MFC units.
Over the next year, on-site routers were replaced with ASUS WL-500g Premium units that ran OpenWRT. Over the next few years, tinc was combined with quagga and/or babel to maintain site-to-site connectivity. Spare routers were kept; that could be re-configured and mailed out with ease.
Around 2010-2011, a third party installed a Cisco-based phone solution with T-1 circuits. The local IPv4 networks were fully updated, and this network remained overlaid on that one.
This network remained active until at least 2013 (my departure from the company) and some time afterward. The company later merged with a competitor and folded during COVID.