The phrase "allow it to fall" is correct and usable in written English.
You can use it in contexts where you are giving permission for something to drop or descend, either literally or metaphorically.
Example: "If the project isn't working out, sometimes it's best to allow it to fall and reassess your approach."
Alternatives: "let it drop" or "permit it to descend".
The Bush administration has expended too much political capital on the issue to allow it to fall off the table.
The republican Labour MP declared the Queen's main residence a national monument and said no government would allow it to fall into disrepair.
Faced with a decision either to remove substantial new gun restrictions from the bill or to allow it to fall to a filibuster next week, Senate leaders plan to put it on hold after a scattering of votes Thursday.
The CSI 300 index breached the 3,500 mark – seen by many local investors as a red line the government would not allow it to fall through – and closed down nearly 9% at 3,275.
The leader, Hassan Nasrallah, declared in a televised speech that Hezbollah could become more deeply involved in the future, and warned that Syria had "real friends" who would not allow it "to fall into the hands" of America, Israel and Islamic extremists, the forces that the Syrian government routinely blames for the two-year uprising against it.
A few days before the final collapse on Sunday, Mr Abadi said he would not allow it to fall.
He discovered on arrival that four days earlier the contractors employed by the defendants to dismantle the boiler had allowed it to fall on its side, sustaining injuries.
Ease your grip on the patient's skin, allowing it to fall back to its natural position.
A family from New Jersey had owned the building for decades and had allowed it to fall into disrepair.
Players try to bat the shuttlecock back and forth as many times as possible without allowing it to fall to the ground.
Much of that success came from a policy of tying the Brazilian currency, the real, to the dollar, and allowing it to fall about 7percentt a year.
