"decided that if" is a correct and usable phrase in written English.
Example: The company decided that if they were to meet their target, they needed to hire an additional worker.
Dine decided that "if you wanted to have influence you had to be a fund-raiser".
So regulators decided that if cheese was not made with pasteurized milk, it should be aged.
Mr Szabadi decided that if Rubik and Schadek could do it, then so could he.
"I decided that if my children died I would pick up my gun in revenge".
So he decided that if he couldn't beat them, he would join them.
"I decided that if this was rock'n'roll, they could keep it," recalled Hunter.
Arrowsmith-Young decided that if rats could grow bigger and better brains, so could she.
Clifton said she had decided that if Wightman was deported, she would go with him.
Finally, we decided that if we have Mike Kelley, we absolutely need Baldessari.
Mr. Milloy has decided that if you can't beat 'em, join 'em.
Eventually I decided that, if I couldn't beat the early birds, I would join them.
