If the UK leaves the EU without a deal, you will need to get a new non-EU residence permit within 2 years of the UK leaving the EU. This will protect your rights, including access to healthcare, rights to work and access to social benefits. Your current EU residency document will remain valid in the meantime.
https://www.gov.uk/guidance/living-in-malta
https://www.gov.mt/en/Life%20Events/Pages/Moving%20to%20Malta/Moving-to-Malta.aspx
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