Sec 498A is non-bailable offence, which means granting of bail is not a right of the accused. Section 438 covers grant of bail for non-bailable offence.
Read about anticipatory bail here:
http://ipc498a.wordpress.com/2007/07/14/what-is-anticipatory-bail/
More info on AB here:
http://ipc498a.wordpress.com/2009/07/26/sc-explains-anticipatory-bail-2009/
FIR no pre-requisite for AB
Read link below for actual judgment that FIR is not required to get AB. From same website: "The filing of a First Information Report is not a condition precedent to the exercise of the power under Section 438. The imminence of a likely arrest founded on a reasonable belief can be shown to exist even if an F.I.R. is not yet filed."
http://iitbiimb498a.wordpress.com/fir-no-pre-requisite-for-ab-gurbaksh-singh-sibbia-judgment/
AB varies from state to state
There are differences between courts of various states and depends on judge too on whether s/he grants AB. So it is difficult to give a blanket answer whether you will be able to get AB based only on threat but no written complaint. If you have good evidence of threat surely the case for AB will become much stronger. But overall it is a game of probabilities.
From SIF(Jul09):
Normally the court can give AB if there's a complaint. We've seen few bail apps being rejected in Bangalore since there was no complaint on record. End of the day, it all depends how good your lawyer is and whether he can get you interim AB. In Punjab, it's difficult for boy to get Interim AB but his parents can probably get.
Other tactics for AB for 498A
Anticipatory Bail: If 498A is not filed yet but threat exists. According to some SIFF wisdom (specifically Chennai guys who told this at Bangalore meeting), husband should not apply for AB. Let other family members apply for AB. This may sound like unnecessary sacrifice for nothing. The reasoning behind this is probably more to do with psychology and sociology of gender and police matters. Husband applying for AB may give impression to police and maybe others is that there is definitely some wrongdoing by husband and he is being careful and applying for AB. Whereas applying for family members may give the impression that husband is innocent and applying AB for his family as precaution.
AB if 498A FIR filed already: If you know there is FIR against you, go and take anticipatory bail as soon as possible.. if needed go absconding until you get AB.