What's likelier is the evolution of English into a classical language - which lends its vocabulary to other languages exactly as Latin and Greek did in the past
It may still remain the mother tongue of large sections of UK, US, Canada, and Aus. But not beyond that
German is the most common ancestry in US. Yet most German Americans speak English
As other European migrants did not maintain endogamy in the new world, they lost their lingual identity
Hardly any in India for instance
Sub-saharan Africa to a limited extent, I grant
Unless of course endogamy collapses in a big way - with very high labor mobility and inter-regional marriages
E.g. When a Tamilian marries a Bengali? What is the mother tongue in this household? English? Or Hindi?
I am not sure if Hindi or English will eventually win, in such scenarios.
I suspect it will remain 50-50...though I think Hindi will have an edge over the Germanic language in such households