EDIT: I think I'll refine my prediction a little.
With Rika's operation around the corner, Yuuichi planned a mock wedding with rika. Everyone that Yuuichi and Rika knew attended the mock wedding, which is what you get on the ED. Everything went smoothly, Rika although disappointed that it's just a mock wedding, she's very happy. Yuuichi then promised that after her operation they get married for real.
However on the day of Rika's operation something went horribly wrong. Doctors, nurses and Akikio struggled to save Rika while Rika did her best to stay alive. After hours of waiting the operation was over, Akiko brings bad news, Yuuichi devastated. Akiko explained that Rika had fought the hardest she could for him. Yuuichi let out a sorrow cry, Akiko gave him a hug of comfort.
Yuuichi tried to end his life to join her (wrist slitting, rooftop jump, pill overdose, take your pick
), but was stopped by a voice, Rika! The usual 'keep living on, for my sake', 'you'll find someone better', 'I'll always be with you forever, in your memory and heart' etc lecture given by Rika before she spirited away.
One day Yuuichi had a dream of him in the church, with Akiko and others. A bride enters, reveal herself as Rika, they both exchange their vows and rings and finally a kiss. Back to reality, Yuuichi never woke up ever since. The credits role.
Epilogue, a few years later a girl was hospitalized for some minor sickness and stumble into Yuuichi's ward out of boredom. Yuuichi after all these years finally woke up, and found himself looking at a girl with who was a spltting image of Rika. A new beginning.
Of course that's my wishful thinking.