My prediction -
1) There's something else that's stopping Harry from competing again. Like they said on Ambridge on the Couch, you can't keep a professional event rider from competing (one of the best in the UK, William Fox-Pitt fell and was in a coma in 2015, came 12th in the 2016 Olympics, Tim Skelton is a show jumper but he broke his neck in 2000 and was competing again in 2001... they're worse than farmers for telling them to stop and retire off of injury). I thought it was maybe something cancer-y but after last nights episode I've changed my mind and think it may be some heart condition and he'll be written off from SADS sometime whilst out on a hack with Alice.
2) Brian absolutely will be dead by the end of Spring, looking grey and having chest tightenings - heart attack impending. Hilda will be once more bounced around the place.
3) Martha's new Shetland pony has some horrible underlying condition because he wasn't vetted at sale and needs to be PTS. (I originally thought cushings but apparently my knowledge is too rusty there as it causes weight loss, not weight gain).
4) The sheep will be grazed on the cricket field secretly, then it'll come out, cause a lot of hassle and Ed will sell the whole flock and take up arborism.