Yes it will reach you eventually, but it may take longer as it wont be sorted as quickly without the postcode.

Hi my name is nathan i went 2 the post office yesterday 2 sent a request 2 neighbours cast 2 have a signed autographes i put my address in the other envople i may have forgot 2 put my post code also i did put all of my address on the other envople also i put united kingdom on it aswell put the problem is that i may have forgot put my post code on it. The question is will it still come 2 me if i have forgot put my post code on it :D