In terms of attendance, Eurovision is fairly small - 6,000 spectators at each show, the disruption will be to people going home after the Thursday semi, and the two shows on Saturday.
So those who can't go will be re-selling their tickets, and there will be plenty of locals who will snap them up.
(I have a ticket for the Saturday afternoon show, which I'll now have to sell back, I had pre-booked a hotel for three nights in Wigan (non-refundable), and Advance rail tickets from the south coast to Wigan, out on the Friday which will get refunded, and back on the Monday which won't. So not the happiest of days for me!)