I strongly doubt that scenario. Mitt Romney invoked no enthusiasm in the Republican Party and most Republicans felt that he was at best the lesser of two evils. Had he won in 2012, he would have been a one-termer. With his incompetence (as evidenced by his governorship) and his nature liberalism, his support in the Republican Party would have been weak. Hillary would have crushed Romney in 2016. All those fantasy landslide scenarios that Rachel Maddow swooned over would have come true for Hillary.
1. If we voted for Romney over Obama, and he'd won, there is NO WAY people would have stayed home if Hillary had been on the ticket. Now, if Bernie or some other loser was the nominee, maybe Willard would have lost in 2016. But if the co-head of the Evil Empire was on the ticket, people would have cast a vote against Hillary.
2. The economy was perceived to be - and was - growing in 2016, and no sitting president in modern times has lost re-election when the economy was perceived to be - and was - growing.