The phrase "hence whether" is correct and can be used in written English.
It is often used to refer to the outcome of a situation or implication of a statement. For example: My boss has been giving me more responsibility lately, hence whether I get a promotion or not is still uncertain.
Hence, "whether to continue to detain such an alien and, if so, in what circumstances and for how long" is up to the attorney general, not up to the courts.
Any given orc, for example, could work out which other fighters on the battlefield were in its line of sight, and hence whether it should flee or attack.
"The replies will help national regulatory authorities to define the state of the market within their own member state, and hence whether any operators have significant market power," Ms Reding said.
The dispute centers on whether Carol's short-lived marriage to a commoner was permitted by the constitution of the day, and hence whether the Lambrino line of his family can inherit royal titles and property.
If we wait a year or two, we will have a firmer basis for knowing whether the recent productivity growth can survive a slower economy and hence, whether the projected surpluses will in fact materialize.
Hence, whether or not the final solution is feasible also depends on the choice of.
Hence, whether PKM2 participates in neuropathic pain has caught our most attention.
Hence, whether suspense requires uncertainty is a matter independent of that concerning the conditions necessary for surprise.
Hence, whether Smith does know whether the proposition literally expressed by "Smith knows…" is true may or may not be relevant to John and Mary's concerns.
The prime objective of this paper is to examine the validity of BT and hence whether it is feasible to conduct the transfer process and assist policy making.
Hence, whether a given particular has a given property places no metaphysical constraints on whether that or any other particular has any other property".
