must have, would have

[Mr. X]

Hello,

Is this combination right when a person is addressing another: John must have been ill, or he would have won. (though conversations are present tense, I am assuming this is right)
(and)
Again, in conversation: John will change things in ways you could never have expected. (can 'will' be followed by 'could' like this? Or, must it always be 'would' followed by 'could'?

Mr. X

[bhaisahab]

Hello,

Is this combination right when a person is addressing another: John must have been ill, or he would have won. (though conversations are present tense, I am assuming this is right)
(and)
Again, in conversation: John will change things in ways you could never have expected. (can 'will' be followed by 'could' like this? Or, must it always be 'would' followed by 'could'?

Mr. X

They are both correct.