Here you got a basic example on how to use Inline buttons and a ReplyMarkup at the same time.
I used 2 ButtonGrid controls for this purpose.
One for the ReplyKeyboard and one for the Inline buttons.
The ReplyKeyboard is within the base MultipleChoiceForm class just for reusing a bit of code.
You can put it into all single forms as well, if you wish. Works the same.
Session serialization is enabled by default via the JSON serializer.