"substantially likely" is correct and usable in written English.
You can use it when referring to an event or situation that is likely to occur, but not necessarily certain. For example, "It is substantially likely that the new drug will be approved by the FDA."
Waisel wrote to the court: "In light of the insufficient dose of midazolam, it is substantially likely that McGuire [is at] substantial, palpable, objectively intolerable risk of experiencing the agony and horrifying sensation of unrelenting air hunger.
"Given the defendant's position," the ruling said, "the court is constrained, at this time, to conclude that it is substantially likely that plaintiffs will succeed on the merits.
The judge, Robin J. Cauthron of District Court, issued a preliminary injunction that said provisions of the law were "substantially likely" to be unconstitutional.
Finally, they had to show that they were "substantially likely" eventually to win their case on the merits of their constitutional argument.
Patients can be compensated only if designated physicians certify that toxic materials or other hazards at ground zero were "substantially likely" to have aggravated or caused the cancer.
… It is substantially likely that McGuire will remain awake and actively conscious for up to five minutes, during which he will increasingly experience air hunger as the drugs suppress his ability to breathe".
Sixty-five percent of voters who don't want him confirmed, the survey finds, say the Supreme Court will be very important to deciding their vote in this year's midterms, compared to 50percentt of those who support his confirmation ― a gap that's especially notable because, in the past, Republicans have often been substantially likelier than Democrats to prioritize Supreme Court appointments.
Complaints filed against officers by white people were substantially more likely to be substantiated than those filed by black people or Latinos.
What's more, they were substantially less likely to have become sick, and more likely to report being happy, during their undergraduate years than the other minority students.
Foreign workers are substantially more likely to be under-skilled and substantially less likely to be over-skilled.
Moreover, high-tech establishments have a substantial fraction of scientists, and are substantially more likely to invest in R&D.
