"left undetermined" is correct and can be used in written English.
It is often used to refer to something that has yet to be or cannot be determined. For example, "The cause of the accident was left undetermined."
A suicide might be called a suicide, a homicide, an accident, or left undetermined.
The American official said the envoys agreed that the precise amount of oil would be left undetermined until working groups were established.
While the pathologist noted the "attempted restraint with electronic control device" as a significant condition, the manner of death was left "undetermined".
The water hubs, envisioned in the proposal as a land-based necklace of physical spaces that follows the arc of the breakwaters, are deliberately left undetermined in the design, inviting residents to define both their form and their function.
He and Richard Llewelyn-Davies, the Labour peer and leader of the Milton Keynes planning team (who died in 1981), were both convinced that, in designing a future city, as much as possible should be left undetermined.
There has been much controversy about this bitter conclusion, as the form that it was to take was left undetermined in the notes Flaubert left, though the materials were gathered and have been published.
It also leaves undetermined whose disapproval is at issue what if one person disapproves of an action but someone else approves?
Our present analysis leaves undetermined the position of one key free-living choanozoan lineage (Corallochytrium, whose cell wall hints at a relationship to Ichthyosoporea, though some trees put it nearer choanoflagellates).
In his early papers, he simply left it undetermined whether or not sentences like (4) and (1) say the same thing, although Stalnaker claims that Perry claimed in personal communication that he intended his proposal to be equivalent to the Naive Russellian proposal; see note 11 of Stalnaker 1981.
Unfortunately, because these seminal studies focused on exogenously induced rhythms, this understanding leaves undetermined which endogenous rhythms might govern dynamic cortical networks relevant to conscious perception.
The restrictive, but stable and understood, rigid structures of work are falling away, dissipating career trajectories and leaving their paths undetermined.
