Raila is allowed to do all sort of political acrobatics but nobody else is allowed. Hassan obviously made a wrong bet - and lost to Joho. He thought he could court the Mombasa's Kambas (thro Wiper) to counter Luo-Luhya support for Joho, hopefully split into half the mijikenda & Swahili vote - and give Joho a ran for his money.
Looking at his options btw now and 2022 (when Joho will not ran again) - he can choose to remain in opposition benches, he can choose to join Jubilee or he can choose to return back to civil society & rehash his proposal writing skills.
My selfish advice is to join Jubilee - UhuRuto biggest obstacle remain Joho - they can't seem to crack the mijikenda - so his support would be taken at premium - however due to ICC manenos - UhuRuto may not trust him that much to let him touch the levers of power. He'll get small time job as head of something - like Kenya Maritime Authority.
In the meantime he need to avoid becoming a Miguna Miguna & Raila - talking too much and too badly about everyone.