Whilst tension arose, I do not see Roosevelt marching straight into Mexico unless Carranza officially accepted the alliance. Maybe a troop build up along the border to remind him of all the reasons he declined, but I very much doubt the Mexican-American War 2: Electric Boogalo, will be declared.
Let's go back a bit. Would TR recognize the presidency of Victoriano Huerta ? How would he handle something like the Tampico Affair - would he do more than just occupy Veracruz, or would he be more diplomatic than Wilson and not invade at all.
Cheers,
Nigel.