if you are seated inside the pub you will not really be able to see Illuminations. You really need a table on the patio, and even then if you are seated far back under the awning you will not see some of the higher fireworks displays from your table (this was our experience the last time we had dinner there).
The thing to keep in mind is that there are no guarantees for a table on the patio versus inside the pub - it's all about timing and luck because everyone wants to dine on the patio for Illuminations.
Actually, DH and I much prefer watching Illuminations over by Norway or Mexico, but it's always fun to experience it from someplace new.
Good luck - I hope you get a good spot on your night!