Your visa expires before the decision comes
A national visa expiring mid-case in Warsaw, Poland does not make your stay unlawful. It changes what you can do at a border, which is the real problem.
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National-Visa
Can you leave Poland while your karta pobytu is pending?
Leaving Poland with a residence case open is the easy half. Coming back is the half that strands people — and the certificate is not an entry document.