Doubting Bro: I thought the funds on deposit arrangement was done away with when they told the local congregations that should only keep 5k in their accounts and forward the rest to the WTS?
Effectively, yes.
It appears though not all congregations have dealt with it - it is poosible that some may have forgotten they even had funds-on-deposit (for example, maybe this could have happened if congregations have merged).
The OP letter seems to be 'formal' notification that the arrangment is ending.
If the WT does not hear back, they will send the money back automatically to the congregation's bank account.
Letter, March 29, 2014 - Re: Adjustment to financing Kingdom Hall and Assembly Hall construction worldwide
What should be done with excess congregation funds that are currently being held or that may accumulate in the future?
The elders of congregations having funds on deposit with the branch office should review the balance of such funds and decide if these can be donated in full or in part to the worldwide work and/or Kingdom Hall and Assembly Hall construction worldwide, particularly if these funds were being saved for a future construction project. Periodically, the body of elders may also review the balance of the congregation funds to determine if surplus cash could be sent to the branch office as a donation. The recommendation for such a donation should be presented to the congregation as a one-time resolution. When this resolution is approved by the congregation, the one-time donation to the worldwide work or to Kingdom Hall and Assembly Hall construction worldwide may be added to the monthly resolved amounts sent to the branch office.