So they either keep Signal around and be able to talk to you, or they don’t. They don’t need to stop using WA to use Signal.
If they don’t want to do that, it’d mean that you would have to keep WA around for the one or two contacts you have there (and only there), which is somewhat comparable, actually, if you disregard the “but meta is short for metastasis, actually” bit.
Which one of the two it ends up being is between you and your contacts.
If I understand this document correctly, it would mean that the entire connection somehow gets routed through Meta’s servers. I can fully understand the reluctance of other parties, including Signal, to do that, and I wonder how this is actually compliant with the DMA.