I have a mutant worm with a tc1 transposon insertion (also has the tc1a recognition site and the whole transposon is 1.6kb long). Would there be a possibility that the transposon remains inactive forever? Or does it mean that there is perhaps another mutation elsewhere enabling the stability to this insertion?
An intact transposon could potentially excise itself and insert in another locus. The excision creates a double-stranded break, and this could repair off the homologous chromosome to recopy the transposon back in, or produce a non-homologous end join (NHEJ) that either still results in a loss of function of the gene, or reconstitute function of the gene. If this occurs in the germline, the reversion allele could be transmitted to the next generation. There are mechanisms (i.e. RNAi) that keep transposase activity silent in the germline, but some backgrounds (e.g. RW7000 or mutations in one of a number of mut loci) have high transposase activity, and you would expect infrequent reversions to occur. The WormBook chapter on transposons gives a review:
Generally Tc1 insertions should be very stable in an N2 background. If you need a bona fide null allele, you could first see if an allele already exists in the Mitani or knockout consortium collections. You could make a non-Tc allele with a non-complementation screen using your existing Tc1 insertion (or over a deficiency). Alternatively, you could use Mos excision to copy in a deletion allele using the MosDel approach, or try using Tc1 hop-out to do the same thing, by adapting the MosDel strategy of inserting Cb-unc-119(+). For information on making another allele, see Jorgensen & Mango 2002 (Nature Reviews Genetics 3, 356-369). For info on MosDel, see Frøkjaer-Jensen et al. (2010) (Nat Methods 7(6):451-3).