The Opel Adam (Vauxhall Adam), Opel Karl (Vauxhall Viva), and Opel Cascada (Vauxhall Cascada) are going out of production because they’re GM cars.
And Opel/Vauxhall under Group PSA has to pay a licensing fee for every one sold. They’re also not selling in large enough numbers.
The official line is they’re being axed so it can concentrate on “CO2 compliance and to focus on high volume segment.”
They will stay in production for a little while, and will “remain on sale until the end of 2019”, but “will not be replaced after the end of their life cycles.”
So if you fancy a cheap Chevy Spark sibling (Karl/Viva), a failed Mini and Fiat 500 competitor (Adam), or an affordable convertible (Cascada) bring your negotiating skills out and get into an Opel/Vauxhall dealership soonish.