Well, I finally got my answer - he died in 2004.
http://www.family-announcements.co.uk/cornwallgroup/view/2468032/david-wiseman
Here's most of it:
Originally printed on December 22, 2004 in the Cornwall and Devon Media.
Viewed by 205 Visitors.
WISEMAN, David. Died, aged 88, on the evening of December 17th, 2004, at
St. Johns Hospice, Doncaster. He was dearly loved Husband of the late
Cicely, Father, Father-in-Law, Grandfather and Great Grandfather, Head
Teacher (Oswin Avenue Secondary School, Doncaster, Tolgus School Redruth)
author and a past President of Manchester University Student Union. His
wise nature enriched the lives of all who knew him, family, pupils,
colleagues, creative writing class students, readers of his Children's
stories and readers of his historical romances (as Jane Julian). Mentor
and friend to so many, he was a gentle, special man a radical and a
Manchester United supporter. His life and the lives of all of us who
grew with him serve as their own testament...
(snip)
The strange thing is, searching on 2004 or even 88 doesn't turn up anything
- at least, not in the first two pages of results. So I had to search on
"Doncaster" instead.
And here are ALL his books. For some reason, my first post didn't have
a complete list.
JUVENILES
Jeremy Visick, Houghton, 1981 (published in England as The Fate of
Jeremy Visick, Viking Kestrel, 1982).
Thimbles, Houghton, 1982.
Blodwen and the Guardians, Houghton, 1983.
Adam's Common, Houghton, 1984.
(Under pseudonym Jane Julian) Ellen Bray, Morrow, 1985.
Pudding and Pie, Viking Kestrel, 1986.
Jumping Jack, Blackie, 1988.
A Badge of Honour, Blackie, 1989, published as A Tie to the Past,
Houghton, 1989.
(Under pseudonym Jane Julian) As Wind to Fire, Piatkus, 1989.
The Devil's Cauldron, Hippo, 1989.
Mum's Winning Streak, 1992.
Plus: The Welfare of the School Child, 1969. (I assume it's non-fiction.)
Awards:
"Preis der Leseratten, ZDF T-V, West Germany, 1982, and Horn Book Honor
List citation, both for Jeremy Visick; American Library Association
Notable Book citation for Thimbles."
http://www.goodreads.com/author/show/254604.David_Wiseman
(reader reviews and summaries)
http://www.abebooks.com/servlet/SearchResults?an=%22wiseman+david%22&pics=on&sortby=7
(book covers and a few summaries)
Lenona.