Or you would have the Ethernet situation: a new better tech that is called Ethernet while having mostly nothing to do with the old one, and people migrate to it, and the old tech is eventually not used anymore.
Hardware has the difference that it eventually stops working and/or becomes obsolete, forcing people to migrate to newer models every so often. Code is immortal.
Nevertheless, in Ethernet's case, while it changed backwards incompatibly at the beginning, since then, consumer Ethernet has been backwards compatible all the way from 1990's 10BASE-T (10Mbit) to the still-rare 10GBASE-T (10Gbit). In data centers you have faster variants that require different cables, for routers... but even there I believe the connections to individual servers typically use the old twisted pair.
To follow in the footsteps of the Ethernet situation the new c++ would have to be better enough to make people switch, which I think is unlikely given the number of programs written in the current c++
