"Nearly 5 million British and EU citizens could be stuck in limbo after a no-deal Brexit, a senior EU official has warned, who said it could take several years “to pick up the pieces” of the UK crashing out of the bloc."
See: No quick fix for citizen rights under no-deal Brexit, says EU official (The Guardian, link):
liticians on both sides of the Brexit divide have urged negotiators to ringfence the existing agreement on citizens’ rights if the UK leaves without a deal on 29 March.
The Brexit withdrawal agreement protects most of the rights of the 3.4 million EU citizens in the UK and the 1.3 million British people in the EU. But since MPs rejected the agreement by a crushing majority last month, these protections have been thrown into doubt.