'Ahl Sithee' (I'll see you) is still a common parting around these parts (Lancashire). As is Tha'll not and Tha' won't. I reckon Thees Thous and Thys will continue in the dialect for a long time to come - and long may they live!

I remember my Grandad, on seeing my hair parted down the middle, as was the style around 1968, commenting 'Thi fathers a stafferdshire mon' (Tr: You resemble a man from Staffordshire - why is whole different story!)   

Try to dig up a book by Dave Dutton and Bill Tidy called 'Lancy Spoken 'ere'. I used to have but gave it to a fellow mudcatter from foreign parts (East Midlands if I remember rightly...) to try an' teach 'em 'ow fer't talk proper.

Good luck in the research

Cheers

Dave the Gnome