Ending slur combined with decresc on single note

[Garrett Fitzgerald]

I'm re-setting my wife's part of Grainger's "Irish Tune from County
Derry", because it doesn't have the authentic English-language tempo
and dynamic instructions. Everything went well (I think) until the
last measure, where a slur terminates on a fermata that decrescendoes
from p to ppp. As a first attempt at this, I used

d4( | << d1)\fermata \\ { s4\p\> s8 s s s s s\ppp } >>

which renders the decrescendo well, but warns me of an unterminated
slur. Putting the ending slur outside the brackets didn't work either,
obviously. Does anyone have any thoughts on how to render this
properly? Thanks.