Max 50000 to 60000 would be its milage, bcoz i live in RWP and daily go to university on my car, i drove my last car 60000 kms in 3 years. you can estimate from that.
why you are going for toyota diesel, you should also look for city 2004-05 it is a much better car and you will enjoy it more than corolla, there is nthing special good in corolla, where as sity has a much better engine than corolla, better technology and car looks more beautiful than corolla. decision is yours. no doubt corolla has good market but city has breaken corola's market alot and its market share is grown very much people find no problem in selling their car, but condition is you must have kept you car well maintained and with love.