I think there is deffo not going to be another series but Kevin has already stated he wants a year off (so no filiming this year) and is up for the idea of a one off next year...maybe a Xmas special but I think only if Lawrence Fox will want to do it aswel.
Remember Morse had a few one off specials before the final ep.
Least we all have Endeavour to look forward to later in the year which I assume will have the full 2 hours ep.
With Morse, John said he wanted to do something else, around 1993 when the last 'series' went out. There'd been 7 series - from 1987 - of three or 4 episodes a year, (28 episodes) and that left little time for anything else.
So they offered him Kavanagh and asked him to do one off specials, which is what they did. And there was 4 - in 95, 96, 97 and 98 before the last one was shown in 2000.
Always remember in one of them - can't remember which! - John did it with his 'Kavanagah' hair! lol